Method and system for starting an internal combustion engine

ABSTRACT

A method and a system for starting an internal combustion engine (ICE) having a crankshaft and an electric turning machine (ETM) operatively connected to the crankshaft are disclosed. An absolute angular position of the crankshaft related to a top dead center position of a piston in a combustion chamber of the ICE is determined. Electric power is delivered to the ETM at a first level to rotate the crankshaft. Electric power is then delivered to the ETM at a second level greater than the first level when the piston reaches a predetermined position before the TDC position. Fuel is injected in the combustion chamber after the piston has passed beyond the TDC position. The fuel is then ignited. In an implementation, the ICE is started in less than 110 degrees of rotation of the crankshaft.

CROSS-REFERENCE

The present application claims priority to U.S. Provisional PatentApplication No. 62/458,882, filed Feb. 14, 2017, the entirety of whichis incorporated herein by reference. For purposes of the United States,the present application is a continuation-in-part of InternationalPatent Application No. PCT/IB2016/056824, filed Nov. 11, 2016, whichclaims priority from U.S. Provisional Patent Application No. 62/254,421,filed Nov. 12, 2015, the entirety of which are incorporated byreference.

FIELD OF TECHNOLOGY

The present technology relates to a method and system for starting aninternal combustion engine.

BACKGROUND

In order to start the internal combustion engine of small vehicles, suchas a snowmobile, a recoil starter is sometimes provided. To start theengine, the user pulls on a rope of the recoil starter which causes thecrankshaft of the engine to turn. If the crankshaft turns fast enough,the engine can be started. If not, the rope needs to be pulled againuntil the engine starts.

In order to facilitate the starting of the engine, some vehicles havebeen provided with an electric starting system. This system consists ofan electric motor, known as a starter, which engages and turns a ringgear connected to the crankshaft via a Bendix™ mechanism, when anignition key is turned or a start button is pushed by the user. Thestarter turns the crankshaft fast enough to permit the starting of theengine, and once the engine has started, disengages the ring gear and isturned off. The vehicle has a battery to supply electric current to thestarter in order to turn the crankshaft.

Although it is very convenient for the user, electric starting systemsof the type described above have some drawbacks. The battery, thestarter and their associated components add weight to the vehicle. Aswould be understood, additional weight reduces the fuel efficiency ofthe vehicle and can affect handling of the vehicle. In the case ofsnowmobiles, this weight also makes it more difficult for the snowmobileto ride on top of snow. These electric starting systems also requireadditional assembly steps when manufacturing the vehicle and take uproom inside the vehicle.

To recharge the battery and to provide the electric current necessary tooperate the various components of the vehicle once the engine hasstarted, an electrical generator is operatively connected to thecrankshaft of the engine. As the crankshaft turns the rotor of theelectrical generator, the generator generates electricity.

In recent years, some vehicles have been provided with motor-generatorunits, also called starter-generators, which replace the starter and theelectrical generator. The motor-generator is operatively connected tothe crankshaft in a manner similar to the aforementioned electricalgenerator. The motor-generator unit can be used as a starter or as agenerator. By applying current to the motor-generator unit, themotor-generator unit operates as a starter and turns the crankshaft toenable starting of the engine. When the motor-generator is operated as agenerator, the rotation of the crankshaft causes the motor-generator togenerate electricity. As would be understood, the use of such systemsaddresses some of the deficiencies of starting systems using separatestarters and electrical generators.

In order to start the engine, the torque applied to the crankshaft tomake it turn has to be sufficiently large to overcome the compressioninside the engine's cylinders resulting from the pistons moving up intheir respective cylinders as the crankshaft rotates. In order toprovide this amount of torque, the motor-generator unit needs to besufficiently large to properly operate as a starter.

Another problem relates to the duration of a starting sequence for theinternal combustion engine, which should be as brief as possible.

A further problem concerns the control of the motor-generator. Whenoperating as a starter, the motor-generator generally operates at lowrotational speeds, sufficient to allow the onset of ignition in theinternal combustion engine. This operation requires the provision of acertain voltage to the motor-generator by the electric starting system.When operating as a generator, the motor-generator provides electricpower over a wide range of rotational speeds of the internal combustionengine, oftentimes far exceeding the starting rotational speed. Withoutspecific voltage control solutions, the motor-generator operating athigh rotational speeds could generate voltages that far exceed the needsof the various components of the vehicle.

There is therefore a need for a method and system for starting aninternal combustion engine that address at least some of the aboveinconveniences.

SUMMARY

It is an object of the present technology to ameliorate at least some ofthe inconveniences present in the prior art.

The present technology provides a system supporting an electrical startprocedure for an internal combustion engine (ICE) and a method forelectrical starting the ICE that uses an electric turning machine (ETM)connected to the crankshaft to start the engine. The method permits anelectrical start of the engine using a power source that is smaller andlighter than conventional batteries. A sensor provides, to a controllera reading of an absolute angular position of a crankshaft of the ICE, ora reading of an absolute angular position of a component of the ICE thatrotates in synchrony with the crankshaft. This reading is available whenthe ICE is stopped, at the onset of a start procedure, and when the ICEis running Based on this reading, the controller knows the position of apiston of the ICE. When the ICE is stopped, the piston tends to be in afirst predetermined position because of a configuration of exhaust portsin a cylinder where the piston is located. The controller determines afirst level of torque that will bring the piston from the firstpredetermined position to a second predetermined position near a topdead center (TDC) position. At that time, the controller determines asecond level of torque, greater than the second level of torque, thatwill bring the piston beyond the TDC position. Fuel injection in thecylinder and ignition will take place once the piston has passed the TDCposition.

In a first aspect, the present technology provides a method for startingan internal combustion engine (ICE) having a crankshaft and an electricturning machine (ETM) operatively connected to the crankshaft. Anabsolute angular position of the crankshaft is determined, the absoluteangular position of the crankshaft being related to an angular positionof a rotor of the ETM. Electric power is delivered to the ETM at a firstlevel to rotate the crankshaft. Electric power is delivered to the ETMat a second level greater than the first level when the rotor of the ETMreaches a predetermined angular position.

In some implementations of the present technology, the method furthercomprises calculating the first level of electric power delivery so thatthe ETM generates sufficient torque to rotate the crankshaft until therotor reaches the predetermined angular position; and calculating thesecond level of electric power delivery so that the ETM generatessufficient torque to rotate the crankshaft beyond the predeterminedangular position of the rotor.

In some implementations of the present technology, calculating the firstlevel of electric power delivery comprises using a vector control of thedelivery of electric power at the first level based on apredetermination of the sufficient torque to rotate the crankshaft untilthe rotor reaches the predetermined angular position; and calculatingthe second level of electric power delivery comprises using a vectorcontrol of the delivery of electric power at the second level based on apredetermination of the sufficient torque to rotate the crankshaftbeyond the predetermined angular position of the rotor.

In some implementations of the present technology, the method furthercomprises energizing an absolute position sensor used to determine theabsolute angular position of the crankshaft when the ICE is stopped.

In some implementations of the present technology, the method furthercomprises energizing the absolute position sensor when the crankshaft isrotating.

In some implementations of the present technology, the method furthercomprises gradually increasing the delivery of electric power to the ETMfrom an initial level to the first level before delivering electricpower to the ETM at the second level.

In some implementations of the present technology, the absolute angularposition of the crankshaft is further related to a position of a pistonin a combustion chamber of the ICE in relation to a top dead center(TDC) position of the piston.

In some implementations of the present technology, delivering electricpower to the ETM at the second level starts when the piston reaches apredetermined position before the TDC position; and the method furthercomprises injecting fuel in the combustion chamber of the ICE when thepiston passes the TDC position a first time and igniting the fuel in thecombustion chamber.

In some implementations of the present technology, the method furthercomprises determining the first level of the electric power delivered tothe ETM based on an initial angular position of the crankshaft.

In some implementations of the present technology, the initial angularposition of the crankshaft is a position of the crankshaft when the ICEis stopped.

In some implementations of the present technology, the initial angularposition is in a range between 80 and 100 degrees before the TDCposition.

In some implementations of the present technology, delivering theelectric power to the ETM before the piston reaches the predeterminedposition before the TDC position causes gases to be expelled from thecombustion chamber.

In some implementations of the present technology, the predeterminedposition before the TDC position is determined according to aconfiguration of exhaust ports of the ICE.

In some implementations of the present technology, the predeterminedposition before the TDC position in a range between 0 and 50 degreesbefore the TDC position.

In some implementations of the present technology, the method furthercomprises terminating the delivery of electric power to the ETM afterstarting the ICE.

In some implementations of the present technology, the delivery ofelectric power to the ETM is terminated when a rotational speed of thecrankshaft reaches a minimum threshold.

In some implementations of the present technology, the fuel is ignitedbefore the piston passes the TDC position a second time.

In some implementations of the present technology, the fuel is injectedin the combustion chamber when the position of the piston passes a rangebetween 3 degrees before the TDC position and 7 degrees after the TDCposition.

In some implementations of the present technology, the fuel is ignitedwhen the position of the piston is in a range between 0 and 12 degreesafter the TDC position, ignition of the fuel taking place afterinjection of the fuel.

In some implementations of the present technology, ignition takes placebefore the piston reaches the top of an exhaust port in the combustionchamber of the ICE

In some implementations of the present technology, the first level ofelectric power delivery is calculated so that the ETM generatessufficient torque to rotate the crankshaft until the piston reaches thepredetermined position before the TDC position; and the second level ofelectric power delivery is calculated so that the ETM generatessufficient torque to cause the piston to move beyond the TDC position.

In some implementations of the present technology, determining theabsolute angular position of the crankshaft comprises sensing theabsolute angular position of the crankshaft.

In some implementations of the present technology, the method furthercomprises sensing n absolute angular position of a component of the ICEthat rotates in synchrony with the crankshaft, wherein the component ofthe ICE that rotates in synchrony with the crankshaft is selected fromthe rotor of the ETM, a fuel pump, an oil pump, a water pump, acamshaft, and a balance shaft; and calculating the absolute angularposition of the crankshaft based on the sensed absolute angular positionof the component of the ICE that rotates in synchrony with thecrankshaft.

In a second aspect, the present technology provides a system forstarting an internal combustion engine (ICE) having a crankshaft. Thesystem comprises a power source, an electric turning machine (ETM)adapted for being mounted to the crankshaft, an absolute position sensoradapted for providing an indication of an absolute angular position ofthe crankshaft, the absolute angular position of the crankshaft beingrelated to an angular position of a rotor of the ETM, and an enginecontrol unit (ECU) operatively connected to the absolute positionsensor. The ECU is adapted for determining the absolute angular positionof the crankshaft based on the indication provided by the absoluteposition sensor. The ECU is further adapted for controlling a deliveryof electric power from the power source to the ETM at a first level torotate the crankshaft and at a second level greater than the first levelwhen the rotor of the ETM reaches a predetermined angular position.

In some implementations of the present technology, the ECU is furtheradapted for: calculating the first level of electric power delivery sothat the ETM generates sufficient torque to rotate the crankshaft untilthe rotor reaches the predetermined angular position; and calculatingthe second level of electric power delivery so that the ETM generatessufficient torque to rotate the crankshaft beyond the predeterminedangular position of the rotor.

In some implementations of the present technology, the ECU implements avector control of the delivery of electric power at the first levelbased on a predetermination of the sufficient torque to rotate thecrankshaft until the rotor reaches the predetermined angular position;and the ECU implements a vector control of the delivery of electricpower at the second level based on a predetermination of the sufficienttorque to rotate the crankshaft beyond the predetermined angularposition of the rotor.

In some implementations of the present technology, the absolute angularposition of the crankshaft is further related to a position of a pistonin a combustion chamber of the ICE in relation to a top dead center(TDC) position of the piston.

In some implementations of the present technology, the delivery ofelectric power from the power source to the ETM at the second levelstarts when the piston reaches a predetermined position before the TDCposition; and the ECU is further adapted for controlling an injection offuel in the combustion chamber of the ICE when the piston passes the TDCposition a first time, and for controlling ignition of the fuel in thecombustion chamber.

In some implementations of the present technology, the ETM is adaptedfor being coaxially mounted to the crankshaft.

In some implementations of the present technology, the absolute positionsensor is adapted for sensing the absolute angular position of thecrankshaft.

In some implementations of the present technology, the absolute positionsensor is adapted for sensing an angular position of a component of theICE that rotates in synchrony with the crankshaft, wherein the componentof the ICE that rotates in synchrony with the crankshaft is selectedfrom the rotor of the ETM, a fuel pump, an oil pump, a water pump, acamshaft, and a balance shaft; and the ECU is adapted for calculatingthe absolute angular position of the crankshaft based on the sensedabsolute angular position of the component of the ICE that rotates insynchrony with the crankshaft and based on a mechanical relationshipbetween the crankshaft of the component of the ICE that rotates insynchrony with the crankshaft.

In some implementations of the present technology, the absolute positionsensor is permanently connected to the power source.

In some implementations of the present technology, the absolute positionsensor is energized by the power source at the onset of a startprocedure for the ICE.

In a third aspect, the present technology provides an internalcombustion engine

(ICE) comprising a crankshaft, a first cylinder, a cylinder headconnected to the first cylinder, a piston operatively connected to thecrankshaft and disposed in the first cylinder. The first cylinder, thecylinder head and a crown of the first piston define a first variablevolume combustion chamber therebetween. The ICE further comprises asystem for starting the ICE. The system comprises a power source, anelectric turning machine (ETM) adapted for being mounted to thecrankshaft, an absolute position sensor adapted for providing anindication of an absolute angular position of the crankshaft, theabsolute angular position of the crankshaft being related to an angularposition of a rotor of the ETM, and an engine control unit (ECU)operatively connected to the absolute position sensor. The ECU isadapted for determining the absolute angular position of the crankshaftbased on the indication provided by the absolute position sensor. TheECU is further adapted for controlling a delivery of electric power fromthe power source to the ETM at a first level to rotate the crankshaftand at a second level greater than the first level when the rotor of theETM reaches a predetermined angular position. The absolute angularposition of the crankshaft is related to a position of the first pistonin the first combustion chamber.

In some implementations of the present technology, the ICE furthercomprises: a direct fuel injector operatively connected to the ECU; andan ignition system operatively connected to the ECU; wherein the ECU isadapted for causing the direct fuel injector to inject the fuel in thefirst combustion chamber and for causing the ignition system to ignitethe fuel.

In some implementations of the present technology, the ICE furthercomprises: a second cylinder; and a second piston operatively connectedto the crankshaft and disposed in the second cylinder, the secondcylinder, the cylinder head and a crown of the second piston defining asecond variable volume combustion chamber therebetween; wherein when thefirst piston compresses gases in the first combustion chamber, thesecond piston expands the volume of the second combustion chamber.

In a fourth aspect, the present technology provides a method forstarting an internal combustion engine (ICE) having a crankshaft and anelectric turning machine (ETM) operatively connected to the crankshaft.An absolute position sensor adapted for providing an indication of anangular position of a rotor of the ETM is energized. A current isapplied to the ETM to generate a torque sufficient to rotate thecrankshaft.

In some implementations of the present technology, the absolute positionsensor provides the indication of the angular position of the rotor ofthe ETM in signals sent to a controller; and the controller calculateson an ongoing basis the actual angular position of the rotor of the ETMbased on the signals from the absolute position sensor.

In some implementations of the present technology, applying a current tothe ETM further comprises: initially applying a first current to theETM; and subsequently applying to the ETM a second current greater thanthe first current when the angular position of the rotor of the ETMpasses beyond a predetermined angular position.

In some implementations of the present technology, the method furthercomprises receiving at a controller a start command for the ICE.

In some implementations of the present technology, the method furthercomprises: determining an initial angular position of the rotor of theETM; and determining a first amount of torque to be supplied by the ETMto the crankshaft based in part on the initial angular position of therotor of the ETM.

In some implementations of the present technology, the method furthercomprises: determining a second angular position of the rotor of theETM, the second angular position indicating that the rotor of the ETMhas passed a first predetermined angular position; and determining asecond amount of torque to be supplied by the ETM to the crankshaftbased in part on the second angular position of the rotor of the ETM,the second amount of torque being greater than the first amount oftorque.

In some implementations of the present technology, the method furthercomprises: determining a third angular position of the rotor of the ETM,the third angular position indicating that the rotor of the ETM haspassed a second predetermined angular position, the second predeterminedangular position being a top dead center (TDC) position of a pistonwithin a combustion chamber; and injecting fuel in the combustionchamber of the ICE.

In some implementations of the present technology, the method furthercomprises: determining a fourth angular position of the rotor of theETM, the fourth angular position indicating that the rotor of the ETMhas passed a third predetermined angular position, the thirdpredetermined angular position being after the second predeterminedangular position; and igniting the fuel in the combustion chamber of theICE.

In some implementations of the present technology, the fourth angularposition is less than 110 degrees of rotation of the crankshaft beyondthe initial angular position.

In some implementations of the present technology, the fourth angularposition is selected so that ignition takes place before opening of anexhaust port in the combustion chamber of the ICE.

In a fifth aspect, the present technology provides an internalcombustion engine (ICE) comprising a crankshaft, a cylinder headdefining in part a variable combustion chamber of the ICE, a direct fuelinjector mounted on the cylinder head, a power source, an electricturning machine (ETM) adapted for rotating the crankshaft, an absoluteposition sensor adapted for providing an indication of an angularposition of a rotor of the ETM and an engine control unit (ECU)operatively connected to the absolute position sensor. The ECU isadapted for vector controlling a delivery of electric power from thepower source to the ETM based on the angular position of the rotor ofthe ETM and for causing the direct fuel injector to inject fuel directlyin the combustion chamber at a time selected based on the angularposition reached by the rotor of the ETM.

In some implementations of the present technology, the ECU causes thedelivery of electric power from the power source to the ETM to generatea first level of torque until the rotor of the ETM reaches a firstpredetermined position and then to generate a second level of torquegreater than the first level of torque as the rotor of the ETM rotatesbeyond the first predetermined position.

In some implementations of the present technology, the ECU causes thedirect fuel injector to inject fuel directly in the combustion chamberafter the ETM has reached the first determined position.

In some implementations of the present technology, the absolute angularposition of the rotor of the ETM is related to a position of a piston inthe combustion chamber, injection of the fuel taking place when thepiston passes at a top dead center position within the combustionchamber.

In some implementations of the present technology, the ECU causes anignition of the fuel after injection of the fuel.

In a sixth aspect, the present technology provides a method forcontrolling delivery of electric power between a power source and anelectric turning machine (ETM). A start signal is applied to a start-uppower electronic switch to cause turning on of the start-up powerelectronic switch and to allow delivery of electric power from the powersource to the ETM via the start-up power electronic switch. A rechargesignal is applied to a run-time power electronic switch to cause turningon of the run-time power electronic switch and to allow delivery ofelectric power from the ETM to the power source via the run-time powerelectronic switch.

In some implementations of the present technology, the method furthercomprises ceasing application of the start signal to the start-up powerelectronic switch when applying the recharge signal to the run-timepower electronic switch.

In some implementations of the present technology, turning on of thestart-up power electronic switch further comprises repeatedly turning onand off the start-up power electronic switch to limit the delivery ofelectric power from the power source to the ETM.

In some implementations of the present technology, the start signal isrepeatedly applied and released to cause repeatedly turning on and offthe start-up power electronic switch.

In some implementations of the present technology, the start signal isvaried according to a pulse width modulation mode.

In some implementations of the present technology, the method furthercomprises providing a current limiting circuit connected in series withthe run-time power electronic switch to limit delivery of electric powerfrom the ETM to the power source.

In some implementations of the present technology, the method furthercomprises, before applying the start signal to the start-up powerelectronic switch, applying and then releasing an initiation signal tothe run-time power electronic switch

In some implementations of the present technology, the start signal isapplied to the start-up power electronic switch via a first driver andthe recharge signal is applied to the run-time power electronic switchvia a second driver.

In a seventh aspect, the present technology provides a circuitcomprising a discharging circuit and a charging circuit. The dischargingcircuit comprises a start-up power electronic switch adapted forallowing delivery of electric power from a power source to an electricturning machine (ETM) via the start-up power electronic switch when thestart-up power electronic switch is turned on. The charging circuitcomprises a run-time power electronic switch adapted for allowingdelivery of electric power from the ETM to the power source via therun-time power electronic switch when the run-time power electronicswitch is turned on.

In some implementations of the present technology, the dischargingcircuit further comprises a first driver adapted for receiving a startsignal and to forward the start signal to the start-up power electronicswitch; and the charging circuit further comprises a second driveradapted for receiving a recharge signal and to forward the rechargesignal to the run-time power electronic switch.

In some implementations of the present technology, the circuit furthercomprises a control unit adapted for applying the start signal to thefirst driver and for applying the recharge signal to the second driver.

In some implementations of the present technology, the control unit isfurther adapted for ceasing application of the start signal to thestart-up power electronic switch when applying the recharge signal tothe run-time power electronic switch.

In some implementations of the present technology, the control unit isfurther adapted for repeatedly applying and releasing the start signalto the first driver to limit the delivery of electric power from thepower source to the ETM.

In some implementations of the present technology, the control unit isfurther adapted for varying the start signal according to a pulse widthmodulation mode.

In some implementations of the present technology, the charging circuitfurther comprises a current limiting circuit connected in series withthe run-time power electronic switch and adapted for limiting deliveryof electric power from the ETM to the power source.

In some implementations of the present technology, the control unit isfurther adapted for applying and then releasing an initiation signal tothe run-time power electronic switch before applying the start signal tothe start-up power electronic switch.

Additional and/or alternative features, aspects and advantages ofimplementations of the present technology will become apparent from thefollowing description, the accompanying drawings and the appendedclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present technology, as well as otheraspects and further features thereof, reference is made to the followingdescription which is to be used in conjunction with the accompanyingdrawings, where:

FIG. 1 is a right side perspective view of a snowmobile;

FIG. 2 is a perspective view taken from a front, left side of aninternal combustion engine of the snowmobile of FIG. 1;

FIG. 3A is a rear elevation view of the engine of FIG. 2;

FIG. 3B is a rear elevation view of another internal combustion enginethat may be installed in the snowmobile of FIG. 1;

FIG. 4A is a cross-sectional view of the engine of FIG. 2 taken throughline 4-4 of FIG. 3, showing a piston at its top dead center position;

FIG. 4B is a cross-sectional view of the engine of FIG. 3B, showing apiston in its bottom dead center position;

FIG. 4C is another view of the engine of FIG. 3B, showing the locationof a water pump;

FIG. 5 is a cross-sectional view of the engine of FIG. 2 taken throughline 5-5 of FIG. 4A with a drive pulley of a CVT mounted on a crankshaftof the engine;

FIG. 6 is a schematic diagram of components of a control system of theengine of FIG. 2;

FIG. 7 is a block diagram of a dual-strategy control system for deliveryof electric power between the capacitance and the electric turningmachine (ETM) of FIG. 6;

FIG. 8 is a block diagram of an energy management circuit for thecapacitance of FIG. 6;

FIG. 9 is a logic diagram of a method for starting the engine of FIG. 2according to an implementation;

FIG. 10 is a timing diagram showing an example of variations of anengine resistive torque as a function of time along with correspondingengine rotational speed variations;

FIG. 11 is a logic diagram of a method for starting the engine of FIG. 2according to another implementation;

FIG. 12 is a circuit diagram showing connections between the inverter,the capacitance and the motor-generator of FIG. 6;

FIG. 13 is a block diagram of a typical implementation of a vectorcontrol drive;

FIG. 14 is a block diagram of an electric system according to animplementation of the present technology;

FIG. 15 is a timing diagram showing an example of a sequence forchanging the control strategy for the delivery of electric power betweenthe capacitance and the electric turning machine (ETM) along withcorresponding engine rotational speed variations;

FIG. 16 is another timing diagram showing an example of an impact of thecontrol strategies on a current exchanged between the capacitance andthe ETM and on a system voltage;

FIG. 17 is yet another timing diagram showing an example of a variationof torque applied to the ETM during the first control strategy;

FIG. 18 is a sequence diagram showing operations of a method forstarting an internal combustion engine; and

FIG. 19 is a sequence diagram showing operations of a method forcontrolling delivery of electric power between a power source and theETM.

DETAILED DESCRIPTION

The method and system for starting an internal combustion engine (ICE)and the method and system for an assisted start of the ICE will bedescribed with respect to a snowmobile 10. However, it is contemplatedthat the method and system could be used in other vehicles, such as, butnot limited to, on-road vehicles, off-road vehicles, a motorcycle, ascooter, a three-wheel road vehicle, a boat powered by an outboardengine or an inboard engine, and an all-terrain vehicle (ATV). It isalso contemplated that the method and system could be used in devicesother than vehicles that have an internal combustion engine such as agenerator. The method and system will also be described with respect toa two-stroke, inline, two-cylinder internal combustion engine (ICE) 24.However, it is contemplated that the method and system could be usedwith an internal combustion engine having one or more cylinders and, inthe case of multi-cylinder engines, having an inline or otherconfiguration, such as a V-type engine as well as 4-stroke engines.

Vehicle

Turning now to FIG. 1, a snowmobile 10 includes a forward end 12 and arearward end 14 that are defined consistently with a forward traveldirection of the snowmobile 10. The snowmobile 10 includes a frame 16that has a tunnel 18, an engine cradle portion 20 and a front suspensionassembly portion 22. The tunnel 18 consists of one or more pieces ofsheet metal arranged to form an inverted U-shape that is connected atthe front to the engine cradle portion 20 and extends rearward therefromalong the longitudinal axis 23. An ICE 24 (schematically illustrated inFIG. 1) is carried by the engine cradle portion 20 of the frame 16. TheICE 24 is described in greater detail below. Two skis 26 are positionedat the forward end 12 of the snowmobile 10 and are attached to the frontsuspension assembly portion 22 of the frame 16 through a frontsuspension assembly 28. The front suspension assembly 28 includes shockabsorber assemblies 29, ski legs 30, and supporting arms 32. Ball jointsand steering rods (not shown) operatively connect the skis 26 to asteering column 34. A steering device in the form of handlebar 36 isattached to the upper end of the steering column 34 to allow a driver torotate the ski legs 30 and thus the skis 26, in order to steer thesnowmobile 10.

An endless drive track 38 is disposed generally under the tunnel 18 andis operatively connected to the ICE 24 through a CVT 40 (schematicallyillustrated by broken lines in FIG. 1) which will be described ingreater detail below. The endless drive track 38 is driven to run abouta rear suspension assembly 42 for propulsion of the snowmobile 10. Therear suspension assembly 42 includes a pair of slide rails 44 in slidingcontact with the endless drive track 38. The rear suspension assembly 42also includes a plurality of shock absorbers 46 which may furtherinclude coil springs (not shown) surrounding one or more of the shockabsorbers 46. Suspension arms 48 and 50 are provided to attach the sliderails 44 to the frame 16. A plurality of idler wheels 52 are alsoprovided in the rear suspension assembly 42. Other types and geometriesof rear suspension assemblies are also contemplated.

At the forward end 12 of the snowmobile 10, fairings 54 enclose the ICE24 and the CVT 40, thereby providing an external shell that protects theICE 24 and the CVT 40. The fairings 54 include a hood and one or moreside panels that can be opened to allow access to the ICE 24 and the CVT40 when this is required, for example, for inspection or maintenance ofthe ICE 24 and/or the CVT 40. A windshield 56 is connected to thefairings 54 near the forward end 12 of the snowmobile 10. Alternativelythe windshield 56 could be connected directly to the handlebar 36. Thewindshield 56 acts as a wind screen to lessen the force of the air onthe driver while the snowmobile 10 is moving forward.

A straddle-type seat 58 is positioned over the tunnel 18. Two footrests60 are positioned on opposite sides of the snowmobile 10 below the seat58 to accommodate the driver's feet.

Internal Combustion Engine

Turning now to FIGS. 2 to 5, the ICE 24 and the CVT 40 will bedescribed. One version of the ICE 24 is shown on FIGS. 2, 3A, 4A and 5and another version of the ICE 24 is shown on FIGS. 3B, 4B and 4C. Bothversions of the ICE 24 are equivalent and interchangeable in the contextof the present disclosure. The ICE 24 operates on the two-strokeprinciple. The ICE 24 has a crankshaft 100 that rotates about ahorizontally disposed axis that extends generally transversely to thelongitudinal axis 23 of the snowmobile 10. The crankshaft drives the CVT40 for transmitting torque to the endless drive track 38 for propulsionof the snowmobile 10.

The CVT 40 includes a drive pulley 62 coupled to the crankshaft 100 torotate with the crankshaft 100 and a driven pulley (not shown) coupledto one end of a transversely mounted jackshaft (not shown) that issupported on the frame 16 through bearings. The opposite end of thetransversely mounted jackshaft is connected to the input member of areduction drive (not shown) and the output member of the reduction driveis connected to a drive axle (not shown) carrying sprocket wheels (notshown) that form a driving connection with the drive track 38.

The drive pulley 62 of the CVT 40 includes a pair of opposedfrustoconical belt drive sheaves 64 and 66 between which a drive belt(not shown) is located. The drive belt is made of rubber, but it iscontemplated that it could be made of metal linkages or of a polymer.The drive pulley 62 will be described in greater detail below. Thedriven pulley includes a pair of frustoconical belt drive sheavesbetween which the drive belt is located. The drive belt is looped aroundboth the drive pulley 62 and the driven pulley. The torque beingtransmitted to the driven pulley provides the necessary clamping forceon the drive belt through its torque sensitive mechanical device inorder to efficiently transfer torque to the other powertrain components.

As discussed above, the drive pulley 62 includes a pair of opposedfrustoconical belt drive sheaves 64 and 66 as can be seen in FIG. 5.Both sheaves 64 and 66 rotate together with the crankshaft 100. Thesheave 64 is fixed in an axial direction relative to the crankshaft 100,and is therefore referred to as the fixed sheave 64. The fixed sheave 64is also rotationally fixed relative to the crankshaft 100. The sheave 66can move toward or away from the fixed sheave 64 in the axial directionof the crankshaft 100 in order to change the drive ratio of the CVT 40,and is therefore referred to as the movable sheave 66. As can be seen inFIG. 5, the fixed sheave 64 is disposed between the movable sheave 66and the ICE 24.

The fixed sheave 64 is mounted on a fixed sheave shaft 68. The fixedsheave 64 is press-fitted on the fixed sheave shaft 68 such that thefixed sheave 64 rotates with the fixed sheave shaft 68. It iscontemplated that the fixed sheave 64 could be connected to the fixedsheave shaft 68 in other known manners to make the fixed sheave 64rotationally and axially fixed relative to the fixed sheave shaft 68. Ascan be seen in FIG. 5, the fixed sheave shaft 68 is hollow and has atapered hollow portion. The tapered hollow portion receives the end ofthe crankshaft 100 therein to transmit torque from the ICE 24 to thedrive pulley 62. A fastener 70 is inserted in the outer end (i.e. theleft side with respect to FIG. 5) of the drive pulley 62, inside thefixed sheave shaft 68, and screwed into the end of the crankshaft 100 toprevent axial displacement of the fixed sheave shaft 68 relative to thecrankshaft 100. It is contemplated that the fixed sheave shaft 68 couldbe connected to the crankshaft 100 in other known manners to make thefixed sheave shaft 68 rotationally and axially fixed relative to thecrankshaft 100. It is also contemplated that the crankshaft 100 could bethe fixed sheave shaft 68.

A cap 72 is taper-fitted in the outer end of the fixed sheave shaft 68.The fastener 70 is also inserted through the cap 72 to connect the cap72 to the fixed sheave shaft 68. It is contemplated that the cap 72could be connected to the fixed sheave shaft 68 by other means. Theradially outer portion of the cap 72 forms a ring 74. An annular rubberdamper 76 is connected to the ring 74. Another ring 78 is connected tothe rubber damper 76 such that the rubber damper 76 is disposed betweenthe rings 74, 78. In the present implementation, the rubber damper 76 isvulcanized to the rings 74, 78, but it is contemplated that they couldbe connected to each other by other means such as by using an adhesivefor example. It is also contemplated that the damper 76 could be made ofa material other than rubber.

A spider 80 is disposed around the fixed sheave shaft 68 and axiallybetween the ring 78 and the movable sheave 66. The spider 80 is axiallyfixed relative to the fixed sheave 64. Apertures (not shown) are formedin the ring 74, the damper 76, and the ring 78. Fasteners (not shown)are inserted through the apertures in the ring 74, the damper 76, thering 78 and the spider 80 to fasten the ring 78 to the spider 80. As aresult, torque is transferred between the fixed sheave shaft 68 and thespider 80 via the cap 72, the rubber damper 76 and the ring 78. Thedamper 76 dampens the torque variations from the fixed sheave shaft 68resulting from the combustion events in the ICE 24. The spider 80therefore rotates with the fixed sheave shaft 68.

A movable sheave shaft 82 is disposed around the fixed sheave shaft 68.The movable sheave 66 is press-fitted on the movable sheave shaft 82such that the movable sheave 66 rotates and moves axially with themovable sheave shaft 82. It is contemplated that the movable sheave 66could be connected to the movable sheave shaft 82 in other known mannersto make the movable sheave 66 rotationally and axially fixed relative tothe shaft 82. It is also contemplated that the movable sheave 66 and themovable sheave shaft 82 could be integrally formed.

To transmit torque from the spider 80 to the movable sheave 104, atorque transfer assembly consisting of three roller assemblies 84connected to the movable sheave 66 is provided. The roller assemblies 84engage the spider 80 so as to permit low friction axial displacement ofthe movable sheave 66 relative to the spider 80 and to eliminate, or atleast minimize, rotation of the movable sheave 66 relative to the spider80. As described above, torque is transferred from the fixed sheave 64to the spider 80 via the damper 76. The spider 80 engages the rollerassemblies 84 which transfer the torque to the movable sheave 66 withno, or very little, backlash. As such, the spider 80 is considered to berotationally fixed relative to the movable sheave 66. It is contemplatedthat in some implementations, the torque transfer assembly could havemore or less than three roller assemblies 84.

As can be seen in FIG. 5, a biasing member in the form of a coil spring86 is disposed inside a cavity 88 defined radially between the movablesheave shaft 82 and the spider 80. As the movable sheave 66 and themovable sheave shaft 82 move axially toward the fixed sheave 64, thespring 86 gets compressed. The spring 86 biases the movable sheave 66and the movable sheave shaft 82 away from the fixed sheave 64 towardtheir position shown in FIG. 5. It is contemplated that, in someimplementations, the movable sheave 66 could be biased away from thefixed sheave 64 by mechanisms other than the spring 86.

The spider 80 has three arms 90 disposed at 120 degrees from each other.Three rollers 92 are rotatably connected to the three arms 90 of thespider 80. Three centrifugal actuators 94 are pivotally connected tothree brackets (not shown) formed by the movable sheave 66. Each roller92 is aligned with a corresponding one of the centrifugal actuators 94.Since the spider 80 and the movable sheave 66 are rotationally fixedrelative to each other, the rollers 92 remain aligned with theircorresponding centrifugal actuators 94 when the shafts 68, 82 rotate.The centrifugal actuators 94 are disposed at 120 degrees from eachother. The centrifugal actuators 94 and the roller assemblies 84 arearranged in an alternating arrangement and are disposed at 60 degreesfrom each other. It is contemplated that the rollers 92 could bepivotally connected to the brackets of the movable sheave 66 and thatthe centrifugal actuators 94 could be connected to the arms 90 of thespider 80. It is also contemplated that there could be more or less thanthree centrifugal actuators 94, in which case there would be acorresponding number of arms 90, rollers 92 and brackets of the movablesheave. It is also contemplated that the rollers 92 could be omitted andreplaced with surfaces against which the centrifugal actuators 94 canslide as they pivot.

In the present implementation, each centrifugal actuator 94 includes anarm 96 that pivots about an axle 98 connected to its respective bracketof the movable sheave 66. The position of the arms 96 relative to theiraxles 98 can be adjusted. It is contemplated that the position of thearms 96 relative to their axles 98 could not be adjustable. Additionaldetail regarding centrifugal actuators of the type of the centrifugalactuator 94 can be found in International Patent Publication No.WO2013/032463 A2, published Mar. 7, 2013, the entirety of which isincorporated herein by reference.

The above description of the drive pulley 62 corresponds to onecontemplated implementation of a drive pulley that can be used with theICE 24. Additional detail regarding drive pulleys of the type of thedrive pulley 62 can be found in International Patent Publication No. WO2015/151032 A1, published on Oct. 8, 2015, the entirety of which isincorporated herein by reference. It is contemplated that other types ofdrive pulleys could be used.

The ICE 24 has a crankcase 102 housing a portion of the crankshaft 100.As can be seen in FIGS. 2, 3 and 5, the crankshaft 100 protrudes fromthe crankcase 102. It is contemplated that the crankshaft 100 coulddrive an output shaft connected directly to the end of the crankshaft100 or offset from the crankshaft 100 and driven by driving means suchas gears in order to drive the drive pulley 62. It is also contemplatedthat the crankshaft 100 could drive, using gears for example, acounterbalance shaft housed in part in the crankcase 102 and that thedrive pulley 62 could be connected to the counterbalance shaft, in whichcase, the crankshaft 100 does not have to protrude from the crankcase102 for this purpose. A cylinder block 104 is disposed on top of andconnected to the crankcase 102. The cylinder block 104 as shown definestwo cylinders 106A, 106B (FIG. 5). A cylinder head 108 is disposed ontop of and is connected to the cylinder block 104.

As best seen in FIG. 5, the crankshaft 100 is supported in the crankcase102 by bearings 110. The crankshaft 100 has two crank pins 112A, 112B.In the illustrated implementation where the two cylinders 106A, 106B aredisposed in line, the crank pins 112A, 112B are provided at 180 degreesfrom each other. It is contemplated that the crank pins 112A, 112B couldbe provided at other angles from each other to account for othercylinder arrangements, such as in a V-type engine. A connecting rod 114Ais connected to the crank pin 112A at one end and to a piston 116A via apiston pin 118A at the other end. As can be seen, the piston 116A has atleast one ring 117A below its crown and is disposed in the cylinder106A. Similarly, a connecting rod 114B is connected to the crank pin112B at one end and to a piston 116B via a piston pin 118B at the otherend. As can be seen, the piston 116B has at least one ring 117B belowits crown and is disposed in the cylinder 106B. Rotation of thecrankshaft 100 causes the pistons 116A, 116B to reciprocate inside theirrespective cylinders 106A, 106B. The cylinder head 108, the cylinder106A and the crown of the piston 116A define a variable volumecombustion chamber 120A therebetween. Similarly, the cylinder head 108,the cylinder 106B and the crown of the piston 116B define a variablevolume combustion chamber 120B therebetween. It is contemplated that thecylinder block 104 could define more than two cylinders 106, in whichcase the ICE 24 would be provided with a corresponding number of pistons116 and connecting rods 114.

Air is supplied to the crankcase 102 via a pair of air intake ports 122(only one of which is shown in FIG. 4A) formed in the back of thecylinder block 104. A pair of throttle bodies 124 is connected to thepair of air intake ports 122. Each throttle body 124 has a throttleplate 126 that can be rotated to control the air flow to the ICE 24.Motors (not shown) are used to change the position of the throttleplates 126, but it is contemplated that throttle cables connected to athrottle lever could be used. It is also contemplated that a singlemotor could be used to change the position of both throttle plates 126.A pair of reed valves 128 (FIG. 4A) are provided in each intake port122. The reed valves 128 allow air to enter the crankcase 102, butprevent air from flowing out of the crankcase 102 via the air intakeports 122.

As the pistons 116A, 116B reciprocate, air from the crankcase 102 flowsinto the combustion chambers 120A, 120B via scavenge ports 130. Fuel isinjected in the combustion chambers 120A, 120B by direct fuel injectors132 a, 132 b respectively. The direct fuel injectors 132 a, 132 b aremounted to the cylinder head 108. The direct fuel injectors 132 a, 132 bare connected by fuel lines and/or rails (not shown) to one or more fuelpumps (not shown) that pump fuel from a fuel tank 133 (FIG. 1) of thesnowmobile 10. In the illustrated implementation, the direct fuelinjectors 132 a, 132 b are E-TEC™ fuel injectors, however other types ofdirect fuel injectors are contemplated. The fuel-air mixture in thecombustion chamber 120A, 120B is ignited by spark plugs 134 a, 134 brespectively (not shown in FIGS. 2 to 5, but schematically illustratedin FIG. 6). The spark plugs 134 a, 134 b are mounted to the cylinderhead 108.

To evacuate the exhaust gases resulting from the combustion of thefuel-air mixture in the combustion chambers 120A, 120B, each cylinder116A, 116B defines one main exhaust port 136A, 136B respectively and twoauxiliary exhaust ports 138A, 138B respectively. It is contemplated thateach cylinder 116A, 116B could have only one, two or more than threeexhaust ports. It is also contemplated that a decompression system (notshown) may be added to the ICE 24 to allow decompressing the combustionchambers 120A, 120B when the ICE 24 is stopped. The exhaust ports 136A,136B (FIGS. 4A, 4B), 138A, 138B are connected to an exhaust manifold140. The exhaust manifold is connected to the front of the cylinderblock 104. Exhaust valves 142A, 142B mounted to the cylinder block 104,control a degree of opening of the exhaust ports 136A, 136B, 138A, 138B.In the present implementation, the exhaust valves 142A, 142B areR.A.V.E.™ exhaust valves, but other types of valves are contemplated. Itis also contemplated that the exhaust valves 142A, 142B could beomitted.

On FIG. 4A, the piston 116B is shown at its top dead center (TDC)position. FIG. 4B provides a cross-sectional view of the engine of FIG.3B with the piston 116B at its bottom dead center (BDC) position,allowing a better view of the main exhaust port 136B respectively and ofthe auxiliary exhaust port 138B.

An electric turning machine (ETM) is connected to the end of thecrankshaft 100 opposite the end of the crankshaft 100 that is connectedto the drive pulley 62. In the present implementation, the ETM is amotor-generator 144 (FIG. 5), and more specifically a three-phasealternating current motor-generator 144, such as for example a permanentmagnet synchronous motor (PMSM) with interior permanent magnet (IPM) orwith surface mounted permanent magnet (SMPM), or a switched reluctancemotor (SRM). It is contemplated that the motor-generator may include anumber of pole pairs, generating electric power cycling at a rate thatis a multiple of the rotational speed of the crankshaft 100. It isfurther contemplated that other types of motor-generators could be used,including for example multi-phase motor-generators or poly-phasemotor-generators. It is also contemplated that the motor-generator 144could be connected to another shaft operatively connected to thecrankshaft 100, by gears or belts for example. The motor-generator 144,as its name suggests, can act as a motor or as a generator and can beswitched between either functions. Under certain conditions as describedhereinbelow, the motor-generator 144 is operated in motor operatingmode, being powered either by a small battery (not shown) or by acapacitance 145 shown on FIG. 3B.

A battery that is smaller and lighter than one conventionally used forcold starting of the ICE 24 may be used for an electric start procedureand/or for an assisted start procedure that will be describedhereinbelow. Alternatively, the electric start procedure and/or theassisted start procedure may rely on the use of a capacitance 145.Non-limiting examples of capacitances include a high-capacity capacitor,an ultracapacitor (U-CAP), an electric double layer capacitor and asupercapacitor Either the small battery or the capacitance 145 supplieselectric power to the motor-generator 144 for turning the crankshaft100. The capacitance 145 can accumulate relatively large amounts ofenergy. In at least one implementation, the capacitance 145 comprises aplurality of capacitors assembled in series, each capacitor of theseries possibly including several capacitors mounted in parallel so thatthe capacitance 145 can withstand voltages generally within an operatingvoltage range of the direct fuel injectors 132A, 132B. In the context ofthe present disclosure, references are made to the capacitance 145 as asingle unit. Without limitation and for brevity, implementations inwhich the electric start procedure or the assisted start procedure, orboth, are implemented using the capacitance 145 along with themotor-generator 144 will be described hereinbelow.

When operating as a generator, the motor-generator 144 is turned by thecrankshaft 100 and generates electricity that is supplied to thecapacitance 145 and to other electrical components of the ICE 24 and thesnowmobile 10. Electric power is exchanged between the capacitance 145and the motor-generator 144 through an electrical converter. Inimplementations in which the motor-generator 144 is a three-phase motor,the electrical converter is a three-phase inverter 146. Use ofmulti-phase or poly-phase invertors in cooperation with a multi-phase ora poly-phase motor-generator is also contemplated. Control strategies ofthe motor-generator 144 applicable to its motoring and generatingfunctions and the impact of these strategies on the capacitance 145 andon the inverter 146 are described hereinbelow.

As can be seen in FIG. 5, the motor-generator 144 has a stator 148 and arotor 150. The stator 148 is disposed around the crankshaft 100 outsideof the crankcase 102 and is fastened to the crankcase 102. The rotor 150is connected by a keyway to the end of the crankshaft 100 and partiallyhouses the stator 148. A housing 152 is disposed over themotor-generator 144 and is connected to the crankcase 102. A cover 154is connected to the end of the housing 152.

Three starting procedures of the snowmobile 10 may be available to theuser. A first procedure comprises a manual start procedure that relieson the use of a recoil starter 156. A second starting procedurecomprises an electric start procedure. A third starting procedurecomprises an assisted start procedure. One or both of the electric andassisted start procedures may be present in any implementation of thesnowmobile 10. The second and third starting procedures will bedescriber further below. As can be seen in FIG. 5, the recoil starter156 is disposed inside the space defined by the housing 152 and thecover 154, between the cover 154 and the motor-generator 144. The recoilstarter 156 has a rope 158 wound around a reel 160. A ratchetingmechanism 162 selectively connects the reel 160 to the rotor 150. Tostart the ICE 24 using the recoil starter 156 in the manual startprocedure, a user pulls on a handle 163 (FIG. 3A) connected to the endof the rope 158. This turns the reel 160 in a direction that causes theratcheting mechanism 162 to lock, thereby turning the rotor 150 and thecrankshaft 100. The rotation of the crankshaft 100 causes the pistons116A, 116B to reciprocate which permits fuel injection and ignition tooccur, thereby starting the ICE 24. When the ICE 24 starts, the rotationof the crankshaft 100 relative to the reel 160 disengages the ratchetingmechanism 162, and as such the crankshaft 100 does not turn the reel160. When the user releases the handle, a spring (not shown) turns thereel 160 thereby winding the rope 158 around the reel 160.

In the present implementation, the drive pulley 62 and themotor-generator 144 are both mounted to the crankshaft 100. It iscontemplated that the drive pulley 62 and the motor-generator 144 couldboth be mounted to a shaft other than the crankshaft 100, such as acounterbalance shaft for example. In the present implementation, thedrive pulley 62, the motor-generator 144 and the recoil starter 56 areall coaxial with and rotate about the axis of rotation of the crankshaft100. It is contemplated that the drive pulley 62, the motor-generator144 and the recoil starter 56 could all be coaxial with and rotate aboutthe axis of rotation of a shaft other than the crankshaft 100, such as acounterbalance shaft for example. It is also contemplated that at leastone of the drive pulley 62, the motor-generator 144 and the recoilstarter 56 could rotate about a different axis. In the presentimplementation, the drive pulley 62 is disposed on one side of the ICE24 and the motor-generator 144 and the recoil starter 56 are bothdisposed on the other side of the ICE 24. It is contemplated the motorgenerator and/or the recoil starter 56 could be disposed on the sameside of the ICE 24 as the drive pulley 62.

Control System for the Internal Combustion Engine

Available starting procedures of the snowmobile 10 comprise an electricstart procedure, an assisted start procedure and a manual startprocedure. FIG. 6 is a schematic diagram of components of a controlsystem of the engine of FIG. 2. The control of the components used tostart the ICE 24 in the electric start procedure and in the assistedstart procedure is done by an engine control unit (ECU) 164 mounted tothe ICE 24, as shown on FIGS. 3B and 4B. The assisted start procedurewill be explained below. The ECU 164 is also used to control theoperation of the ICE 24 after it has started. The ECU 164 is energizedby the capacitance 145, in a manner that will be described hereinbelow.The ECU 164 is illustrated as a single physical module (later shown inFIG. 14) comprising a single processor (also in FIG. 14), for example asingle microcontroller. Other configurations are within the scope of thepresent disclosure. For instance, it is contemplated that features ofthe ECU 164 may be implemented using a plurality of co-processors, forexample two or more microcontrollers. It is also contemplated that thevarious tasks of the ECU 164 could be split between two or moremicroprocessors integrated in a single electronic module or two or moremicroprocessors distributed among various electronic modules. As anon-limitative example, the single electronic module may comprise afirst processor adapted for controlling a delivery of electric powerfrom the motor-generator 144 to the capacitance 145 and to control thedelivery of electric power from the capacitance 145 to themotor-generator 144, and a second processor adapted for controlling afuel injection function and an ignition function of the ICE. To initiatean electric start procedure or an assisted start procedure of the ICE24, the ECU 164 receives inputs from the components disposed to the leftof the ECU 164 in FIG. 6, some of which are optional and not present inall implementations, as will be described below. Using these inputs, theECU 164 obtains information from control maps 166 as to how thecomponents disposed to the right of the ECU 164 in FIG. 6 should becontrolled in order to start the ICE 24. The control maps 166 are storedin an electronic data storage device, such as an electrically-erasableprogrammable read-only memory (EEPROM) or a flash drive. It iscontemplated that instead of or in addition to the control maps 166, theECU 164 could use control algorithms to control the components disposedto the right of the ECU 164 in FIG. 6. In the present implementation,the ECU 164 is connected with the various components illustrated in FIG.6 via wired connections; however it is contemplated that it could beconnected to one or more of these components wirelessly.

A user actionable electric start switch 168, provided on the snowmobile10, for example a push button mounted on or near the handlebar 36, sendsa signal to the ECU 164 that the user desires the ICE 24 to start whenit is actuated. The electric start switch 168 can also be a switchactuated by a key, a sensor, or any other type of device through whichthe user can provide an input to the ECU 164 that the ICE 24 is to bestarted. In at least one implementation, the electric start switch 168may be a sensor operably connected to the rope 158 of the recoil starter156 and to the ECU 164. Some traction, for example a simple tugging onthe rope 158 by an operator, may be detected by this sensor, resultingin the initiation of the electric start procedure of the ICE 24,provided that all conditions for the electric start procedure arepresent.

A crankshaft position sensor (CPS) 171 and an absolute crankshaftposition sensor (ACPS) 170 are disposed in the vicinity of thecrankshaft 100 in order to sense an absolute position of the crankshaft100. Readings of the CPS 170 are used by the ECU 164 to determine arotational speed of the crankshaft 170. From a manual start or from anassisted start, the CPS 170 becomes energized by an initial rotation ofthe crankshaft 100. Like the ECU 164, the ACPS 170 is energized by thecapacitance 145. In one implementation, the ACPS 170 is electricallyconnected to the capacitance 145 so that the ACPS 170 is constantlyenergized, as long as there is a minimum level of charge in thecapacitance 145. In another implementation, the ACPS 170 becomesenergized by the capacitance 145, via the ECU 164, in the course of astarting procedure, as will be described hereinbelow. In the presentimplementation, the CPS 171 is an inductive position sensor while theACPS 170 is a sin/cos Hall Effect encoder. FIG. 5 shows an example of alocation of a Hall Effect ACPS 170 that is placed at an extremity of thecrankshaft 100 and rotates with the crankshaft 100. The ACPS 170 mayalternatively comprise an optical sensor. FIG. 5 also shows a locationof the CPS 171, placed in a manner where it can track the movement ofthe rotor 150 of the motor-generator 144, the rotor 150 turning insynchrony with and at the same rate as the crankshaft 100. The ACPS 170senses the absolute position of the crankshaft 100 on a continuousbasis, as long as the ACPS 170 is energized from an electric source(shown in later Figures). The ACPS 170 sends a signal representative ofthe absolute position of the crankshaft 100 to the ECU 164. The absoluteposition of the crankshaft 100 provided by the ACPS 170 enables the ECU164 to determine the current position of the pistons 116A, 116B whetherthe crankshaft 100 is rotating, or stopped in any position. Inparticular, the ECU 164 uses the provided absolute position informationto determine the current position of the pistons 116A, 116B in relationto their respective top dead center (TDC) positions. The currentposition of a piston in relation to its TDC position may be expressed interms of degrees of rotation before TDC (BTDC) or after TDC (ATDC).Based on variations of the absolute position of the crankshaft 100received from the ACPS 170, the ECU 164 is also able to determinerotational speed of the crankshaft 100.

It is contemplated that an absolute position sensor (not shown) couldalternatively sense the absolute position of a component of the ICE 24,other than the crankshaft 100, that turns in synchrony with thecrankshaft 100, for example a water pump. FIG. 4C is another view of theengine of FIG. 2, showing the location of a water pump, generally at173. In an implementation, the water pump 173 turns at the same rate asthe crankshaft 100. A magnet 175 is mounted to the water pump 173. AHall effect sensor 177 is in a fixed position and tracks rotationalmovements of the magnet 175 when rotation of the crankshaft 100 causesthe rotation of the water pump 173. Other components of the ICE 24 onwhich the absolute position sensor may be mounted include, for exampleand without limitation, the rotor 150 of the motor-generator 144, a fuelpump, an oil pump, a camshaft (if the ICE is a 4-stroke engine), abalance shaft (these component s are not shown), and the like. In such acase, based on a known mechanical configuration of the ICE 24, the ECU164 can deduce the absolute position of the crankshaft 100 from theabsolute position of this component.

The ECU 164 controls the operation and timing of the direct fuelinjectors 132 a, 132 b and of the spark plugs 134 a, 134 b. To this end,when starting the ICE 24, the ECU 164 uses the absolute position of thecrankshaft 100, obtained from the ACPS 170, to cause the direct fuelinjectors 132 a, 132 b to inject calculated amounts of fuel in theirrespective combustion chambers 120A, 120B a short time after therespective pistons 116A, 116B have reached their TDC positions. The ECU164 then causes the respective spark plugs 134 a, 134 b to ignite thefuel shortly thereafter. As an example and without limitation, injectionin the combustion chamber 120A may take place when the crankshaft 100has rotated until the piston 116A reaches a position in a range of about3 degrees before TDC to 7 degrees after TDC. Ignition by use of thespark plug 134 in the combustion chamber 1220A follows, for example in arange of about 0 to 12 degrees beyond TDC (0 to 12 degrees ATDC) for thepiston 116A. Injection and ignition timings vary according to operatingconditions of the ICE 24.

The assisted start procedure may be initiated, provided that conditionsare met as described hereinbelow, when a rotation of the crankshaft 100is initiated by the user pulling on the rope 158 of the recoil starter156. The CPS 171 wakes up the ECU 164 upon initial rotation of thecrankshaft 100. The ECU 164 in turn causes the capacitance 145 toenergize the ACPS 170, allowing the ACPS 170 to inform the ECU 164 ofthe absolute angular position of the crankshaft 100.

A voltage sensor 167, for example a voltmeter, provides a measurement ofa voltage of the capacitance 145 to the ECU 164. As explained in moredetails hereinbelow, the ECU 164 uses this voltage measurement todetermine whether an energy reserve of the capacitance 145 is sufficientto start the ICE 24 using the electric start procedure or to provideassist using the assisted start procedure.

Optionally, other sensors can be used to determine whether or not theengine can be started using the electric start procedure or the assistedstart procedure as expressed hereinbelow. These optional sensors includefor example an engine temperature sensor 172, an air temperature sensor174, an atmospheric air pressure sensor 176, an exhaust temperaturesensor 178, a timer 180 and an ECU temperature sensor 182.

The engine temperature sensor 172 is mounted to the ICE 24 to sense thetemperature of one or more of the crankcase 102, the cylinder block 104,the cylinder head 108 and engine coolant temperature. The enginetemperature sensor 172 sends a signal representative of the sensedtemperature to the ECU 164.

The air temperature sensor 174 is mounted to the snowmobile 10, in theair intake system for example, to sense the temperature of the air to besupplied to the ICE 24. The air temperature sensor 174 sends a signalrepresentative of the air temperature to the ECU 164.

The atmospheric air pressure sensor 176 is mounted to the snowmobile 10,in the air intake system for example, to sense the atmospheric airpressure. The atmospheric air pressure sensor 176 sends a signalrepresentative of the atmospheric air pressure to the ECU 164.

The exhaust temperature sensor 178 is mounted to the exhaust manifold140 or another portion of an exhaust system of the snowmobile 10 tosense the temperature of the exhaust gases. The exhaust temperaturesensor 178 sends a signal representative of the temperature of theexhaust gases to the ECU 164.

The timer 180 is connected to the ECU 164 to provide information to theECU 164 regarding the amount of time elapsed since the ICE 24 hasstopped. The timer 180 can be an actual timer which starts when the ICE24 stops. Alternatively, the function of the timer 180 can be obtainedfrom a calendar and clock function of the ECU 164 or another electroniccomponent. In such an implementation, the ECU 164 logs the time and datewhen the ICE 24 is stopped and looks up this data to determine how muchtime has elapsed since the ICE 24 has stopped when the ECU 164 receivesa signal from the electric start switch 168 that the user desires theICE 24 to be started.

The ECU temperature sensor 182 is mounted to a physical module (notshown) that includes one or more processors (not shown) configured toexecute the functions of the ECU 164. The ECU temperature sensor 182sends a signal representative of the temperature of that module to theECU 164.

It is contemplated that one or more of the sensors 172, 174, 176, 178,182 and the timer 180 could be omitted. It is also contemplated that oneor more of the sensors 172, 174, 176, 178, 180, 182 and the timer 180could be used only under certain conditions. For example, the exhausttemperature and pressure sensors 178, 180 may only be used if the ICE 24has been recently stopped, in which case some exhaust gases would stillbe present in the exhaust system, or following the first combustion of afuel-air mixture in one of the combustion chambers 120A, 120B.

The ECU 164 uses the inputs received from at least some of the electricstart switch 168, the sensors 167, 170, 171, 172, 174, 176, 178, 182 andthe timer 180 to retrieve one or more corresponding control maps 166 andto control the motor-generator 144, the direct fuel injectors 132 a, 132b, and the spark plugs 134 a, 134 b using these inputs and/or thecontrol maps 166 to start the ICE 24, as the case may be. The inputs andcontrol maps 166 are also used to control the operation of the ICE 24once it has started. Though not shown on FIG. 6 in order to simplify theillustration, the various components of the control system of FIG. 6 areenergized by the capacitance 145.

The ECU 164 is also connected to a display 186 provided on thesnowmobile 10 near the handlebar 36 to provide information to the userof the snowmobile 10, such as engine speed, vehicle speed, oiltemperature, and fuel level, for example.

Turning now to FIG. 7, details of an electronic system for the electricand assisted start procedures for the ICE 24 will now be described. FIG.7 is a block diagram of a dual-strategy control system for delivery ofelectric power between the capacitance and the ETM of FIG. 6. Somecomponents introduced in the foregoing description of FIG. 6 arereproduced in FIG. 7 in order to provide more details on theiroperation.

Electric power is delivered between the capacitance 145 and themotor-generator 144 through the inverter 146. The ECU 164 includes, oris otherwise operatively connected to, a strategy switch 184 that isoperative to change the control strategy for the delivery of electricpower between the capacitance 145 and the motor-generator 144 between atleast two (2) distinct control strategies. The ECU 164 controls theinverter 146 through the strategy switch 184.

To start the ICE 24 using the electric start procedure, the user of thesnowmobile 10 enters an input on the electric start switch 168, forexample by depressing a push button. The ECU 164 is informed of thiscommand In response, the ECU 164 may control a delivery of electricpower from the capacitance 145 to the motor-generator 144 based on apre-determined amount of torque, or torque request, sufficient to causerotation of the crankshaft 100 for starting the ICE 24. In a variant,the ECU 164 may determine the torque request. The determination of thetorque request is made considering that ICE 24 is expected to have ahighly irregular resistive torque; alternatively, instead of determiningthe torque request, the ECU 164 may determine a speed request applicableto the crankshaft 100 to control an amount of power that that themotor-generator 144 should apply to the crankshaft 100 for starting theICE 24. A voltage of the capacitance 145 is sensed by the voltage sensor167 and provided to the ECU 164. If this voltage is below an electricstart voltage threshold V_(MinE), which is a minimum voltage of thecapacitance 145 for the electric start procedure, the ECU 164 determinesthat the capacitance 145 does not hold sufficient energy to provide thetorque request, or the speed request, sufficient to start the ICE 24using the electric start procedure. Consequently, the ECU 164 does notallow starting the ICE 24 using the electric start procedure and causesthe display 186 to show a “manual start” indication or an “assistedstart” indication, in implementations where this option is available.Generally speaking, the electric start voltage threshold V_(MinE) isbased on a determination of a sufficient charge of the capacitance 145allowing a successful electric start procedure in most operatingconditions. If this minimum voltage threshold for the electric startprocedure is met, the ECU 164 causes delivery of electric power from thecapacitance 145 to the motor-generator 144, via the inverter 146, in afirst control strategy, initiating a rotation of the crankshaft 100. TheECU 164 also causes the direct fuel injectors 132 a and 132 b to injectfuel directly in the combustion chambers 120A, 120B and causes the sparkplugs 134 a and 134 b to ignite the fuel in the combustion chambers120A, 120B. As mentioned hereinabove, the ICE 24 may comprise one ormore cylinders and the mention of two (2) combustion chambers 120A and120B is for explanation purposes only. If these operations aresuccessful, the rotation of the crankshaft 100 reaches a minimumrevolution threshold corresponding to a successful start of the ICE 24.Thereafter, when a speed of the crankshaft 100 is equal to or above theminimum revolution threshold, the ECU 164 controls the delivery ofelectric power from the motor-generator 144 to the capacitance 145,still via the inverter 146, to cause charging of the capacitance 145.The delivery of electric power from the motor-generator 144 to thecapacitance 145 generally occurs in a second control strategy distinctfrom the first control strategy. A variant in which the delivery ofelectric power from the motor-generator 144 to the capacitance 145occurs in the first control strategy at low revolution speeds of thecrankshaft 100, or under low throttle demands, and in the second controlstrategy at high revolution speeds of the crankshaft 100 is alsocontemplated.

A current sensor 188 may be used to optimize the capacitance 145 currentconsumption and optimize its energy usage. The current sensor 188provides to the ECU 164 an indication of the energy from the capacitance145 being consumed during the electric start procedure. In animplementation, the current sensor 188 comprises a combination of phasecurrent sensors (not explicitly shown) provided on two (2) phases of themotor-generator 144. Encoding of measurements from these two (2) phasecurrent sensors provide a good estimation of a current flowing betweenthe capacitance 145 and the motor-generator 144. As shown on FIG. 13,current measurements may be obtained on all three (3) phases of themotor-generator 144. The capacitance 145 energy usage can alternativelybe optimized without current sensors, for example, an open loop approachhaving a predetermined torque request pattern being applied by the ECU164 to drive all cranking sequences can be used. It is also possible tooptimize the energy usage of the capacitance 145 based on a speedrequest with well-tuned regulators or based on a predetermined patternof multistep speed requests.

Electric start of the ICE 24 may fail although initial conditions forthe electric start procedure were initially present. This may occur forinstance if, while electric power is being delivered from thecapacitance 145 to the motor-generator 144, the voltage sensor 167detects that the voltage of the capacitance 145 falls below a residualvoltage threshold V_(MinR), lower than the electric start voltagethreshold V_(MinE), before the rotational speed of the crankshaft 100reaches the minimum revolution threshold corresponding to the successfulstart of the ICE 24. Under such conditions, the ECU 164 ceases thedelivery of power from the capacitance 145 to the motor-generator 144and causes the display 186 to provide a manual start indication or anassisted start indication, in implementations where this option isavailable. Generally speaking, the residual voltage threshold V_(MinR)corresponds to a minimum charge of the capacitance 145 that is expectedto suffice in allowing the injection and ignition of fuel injection inthe combustion chambers 120A, 120B while continuing the rotation of thecrankshaft 100.

To start the ICE 24 using the assisted start procedure, the user of thesnowmobile 10 pulls on the rope 158 of the recoil starter 156,initiating a rotation of the crankshaft 100. The CPS 171 wakes up theECU 164 upon initial rotation of the crankshaft 100 and the ACPS 170then informs the ECU 164 of the absolute angular position of thecrankshaft 100. In response, the ECU 164 may control a delivery ofelectric power from the capacitance 145 to the motor-generator 144 toassist the rotation of the crankshaft 100 for starting the ICE 24.Optionally, a voltage of the capacitance 145 is sensed by the voltagesensor 167 and provided to the ECU 164. In this case, if this voltage isbelow an assisted start voltage threshold V_(MinA), which is a minimumvoltage of the capacitance 145 for the assisted start procedure, the ECU164 determines that the capacitance 145 does not hold sufficient energyto assist starting the ICE 24 and the ECU 164 does not allow startingthe ICE 24 using the assisted start procedure, instead causing thedisplay 186 to show a “manual start” indication. Generally speaking, theassisted start voltage threshold V_(MinA) is based on a determination ofa sufficient charge of the capacitance 145 allowing a successfulassisted start procedure in predetermined operating conditions. Inimplementations where both electric and assisted start procedures arepresent, the assisted start voltage threshold V_(MinA) is lower than theelectrical start voltage threshold V_(MinE). If this minimum voltagethreshold for the assisted start procedure is met, the ECU 164 causesdelivery of electric power from the capacitance 145 to themotor-generator 144, via the inverter 146, in the first controlstrategy, assisting the rotation of the crankshaft 100. The ECU 164 alsocauses the direct fuel injectors 132 a and 132 b to inject fuel directlyin the combustion chambers 120A, 120B and causes the spark plugs 134 aand 134 b to ignite the fuel in the combustion chambers 120A, 120B. Asmentioned hereinabove, the ICE 24 may comprise one or more cylinders andthe mention of two (2) combustion chambers 120A and 120B is forexplanation purposes only. If these operations are successful, therotation of the crankshaft 100 reaches a minimum revolution thresholdcorresponding to a successful start of the ICE 24. Thereafter, operationof the ICE 24 is as expressed in the foregoing description to theelectrical start procedure.

FIG. 8 is a block diagram of an energy management circuit for thecapacitance 145 of FIG. 6. A circuit 200 shows how, in animplementation, the CPS 171, the ECU 164 and the capacitance 145 areelectrically connected. In the case of the electric start procedure, theconnection between the capacitance 145 and the ECU 164 is effected usingthe electric start switch 168, which is shown as a pushbutton. In thecase of the assisted start procedure and in the case of the manual startprocedure, the connection is effected by a signal from the CPS 171,which is present at the onset of the rotation of the crankshaft 100. Thecapacitance 145 is illustrated as a sum of smaller capacitors 202connected in series. As mentioned earlier, each of these smallercapacitors 202 may actually consist of a plurality of capacitorsconnected in parallel. Each of the smaller capacitors 202 can withstanda relatively low voltage applied thereon. The capacitance 145 formed bythe sum of the smaller capacitors 202 in series can withstand thenominal voltage of the circuit 200, which is also the nominal voltage ofthe electrical systems of the snowmobile 10, with the addition of asafety margin for occasional overvoltage

The circuit 200 provides an output voltage between a lead 208 and aground reference 210 when the circuit 200 is active. When the circuit200 is inactive, the capacitance 145 is disconnected from the groundreference 210 by power electronic switches, for example metal-oxidesemiconductor field effect transistors (MOSEFT) Q1 and Q2 which are, atthe time, turned off and therefore open circuit. Substituting a bipolartransistor, for example an insulated gate bipolar transistor (IGBT), forthe MOSFETs Q1 and Q2 is also contemplated. The available voltage of thecapacitance 145 is defined between terminals 208 and 210 that areelectrically connected to the voltage sensor 167 shown on earlierFigures.

A capacitor C1 shown on FIGS. 3B and 4B and schematically illustrated onFIG. 8 is present between the lead 208 and the ground reference 210. Therole of the capacitor C1 is to filter voltage variations from thecapacitance 145 for the benefit of the various electrical components ofthe snowmobile 10, including for example the direct fuel injectors 132 aand 132 b, headlights, and the like. The capacitor C1 may be omitted insome implementations. The voltage between the lead 208 and the groundreference 210, which is a system voltage for the snowmobile 10, isessentially the same as the nominal voltage of the capacitance 145,although operating voltages between different system states may not beconstant at all times.

When the ICE 24 has been stopped for a long time, more than a few hoursfor example, the voltage on the capacitance 145 falls below the electricstart voltage threshold V_(MinE) and below the assisted start voltagethreshold V_(MinA), and the circuit 200 is not energized. Resorting tothe manual start procedure is therefore required for starting the ICE24. When the ICE 24 has been stopped for a relatively short time, aduration of which depends in large part on the energy storage capacityof the capacitance 145, the voltage on the capacitance 145 may be equalto or above the electric start voltage threshold V_(MinE), in which casethe electric start procedure is available. If the voltage of thecapacitance 145 is lower than the electric start voltage thresholdV_(MinE) while at least equal to or greater than the assisted startvoltage threshold V_(MinA), the assisted start procedure may beavailable. The assisted start procedure is described in more detailshereinbelow.

When the voltage of the capacitance 145 is at least equal or greaterthan the electric start voltage threshold V_(MinE), depressing theelectric start switch 168 (pushbutton) by the user invokes the electricstart procedure. This user action is sensed by a start command detector212 of the ECU 164. When the user initiates a manual start procedure oran assisted start procedure, the CPS 171 is energizes and sends aninitiating signal to the start command detector 212.

The start command detector 212 wakes up the ECU 164. At the same time,electrical power starts being provided from the capacitance 145 to theECU 164. Depending on specific implementations, the start commanddetector 212 may accept a simple brief electrical contact provided bythe electric start switch 168 to initiate the electric start procedure.The start command detector 212 may alternatively require the electricstart switch 168 to be depressed for a few seconds. After sensing theelectric start command or the initiating signal, the start commanddetector 212 sends a signal to a wake up circuit 214 of the ECU 164. Thewake up circuit 214 controls the following operations.

Initially, the wake up circuit 214 applies an initiation signal 220 to adriver 216 of the transistor Q1, which is a run-time power electronicswitch. The driver 216 further applies the initiation signal to thetransistor Q1, causing the transistor Q1 to turn on, allowing thecapacitance 145 to start charging the capacitor C1 via a currentlimiting circuit 224. As soon as a voltage starts being established inthe capacitor C1, the wake up circuit 214 terminates the initiationsignal 220 and applies a start signal 221 to a driver 217 of thetransistor Q2, which is a start-up power electronic switch, effectivelyplacing the capacitance 145 in parallel with the capacitor C1 to furthercharge the capacitor C1. In an implementation, the wake up circuit 214controls the driver 217 to repeatedly turn on and off the transistor Q2at a high frequency in order to prevent excessive current flowing fromthe capacitance 145 to the capacitor Cl. For example, the wake upcircuit 216 of the ECU 164 may vary the start signal 221 according to apulse width modulation (PWM) mode. Electrical conduction through thetransistor Q2 may be controlled in a small duty cycle at first, the dutycycle increasing as a voltage difference between the capacitor C1 andthe capacitance 145 decreases. Regardless, the capacitor C1 rapidlycharges to reach the voltage of the capacitance 145. The capacitance 145voltage may reduce slightly as a result from this voltage equalization,but this effect is limited by the fact that the capacitor C1 is muchsmaller than the capacitance 145. After the capacitor C1 has beencharged, an electric connection is made between the lead 208 and thevarious sensors 167, 170, 171, 172, 174, 176 and 182, the timer 180, andother components of the snowmobile 10 that may be energized at the sametime or later, according to the needs of the application.

In an implementation where the capacitor C1 is not present, the wake upcircuit 214 may not apply the initiation signal 220 to the driver 216.In that case, in response to the signal from the start command detector212, the wake up circuit 214 simply applies the start signal 221 to thedriver 217 of the transistor Q2 so that the capacitance 145 voltagebecomes available at the lead 208.

In an implementation where the ACPS 170 is not permanently connected tothe capacitance 145, it becomes energized at the onset of a startprocedure, through the lead 208 following this voltage equalization, soto enable the reading of the current (i.e. initial) absolute angularposition of the crankshaft. This reading is provided by the ACPS 170 tothe ECU 164. The electric start then continues with the ECU 164controlling the delivery of power from the capacitance 145 to themotor-generator 144 via the lead 208, which is connected to the inverter146 in one of the manners described in relation to the followingFigures. The ECU 164 may control the transistor Q2 in the PWM mode tolimit a level of electric power delivery from the capacitance 145 to themotor-generator 144.

Once the electric start procedure has been successfully executed, as theICE 24 is running at idle, the motor-generator 144 may initially have alimited power generating capacity. Accessories of the snowmobile 10,including for example the direct fuel injectors 132 a and 132 b andheadlights, require a certain amount of power. It is more critical tothe operation of the vehicle to power these accessories than rechargingthe capacitance 145. To avoid an excessive drop of the voltage of thecapacitor C1, at the lead 208, while the ICE 24 is idling or running,the ECU 164 may optionally control the driver 217 to turn off thetransistor Q2 until the crankshaft 100 rotates at more than apredetermined revolution threshold.

Once the ICE 24 has acquired a sufficient speed, the voltage at the lead208 being now sufficient, the ECU 164 stops the start signal 221 to thedriver 217, causing the turning off (opening) of the transistor Q2. TheECU 164 also sends a recharge signal 222 to the driver 216 of thetransistor Q1. The driver 216 further applies the recharge signal to thetransistor Q1, causing turning on (closing) of the transistor Q1. Thetransistor Q1 is connected in series with the current limiting circuit224. The transistor Q1 effectively places the capacitance 145 in contactwith the capacitor C1, the current limiting circuit 224 regulating thecharging rate of capacitance 145 while respecting the electrical poweravailability at any speed of the ICE 24. In an implementation, thecurrent limiting circuit 224 comprises a resistor or an inductor (notshown).

In an alternate implementation, the circuit 200 includes a single driver217 and a single transistor Q2 and does not include a current limitingcircuit. The wake up circuit 214 intermittently applies the start signal221 to the driver 217 of the transistor Q2, for example according to aPWM mode, so that the voltage gradually increases at the lead 208 untilit becomes substantially equal to the voltage of the capacitance 145. Inthe same implementation, the recharge signal 222 is also applied to thedriver 216 of the transistor Q2. Instead of using the current limitingcircuit 224 to regulate the charging rate of the capacitance 145, therecharge signal 222 may also be applied to the driver 217 according to aPWM mode. As will be expressed hereinbelow, a control strategy of thedelivery of electric power from the motor-generator 144 to thecapacitance 145 may alternatively be used to regulate the charging rateof the capacitance 145.

The ECU 164 may optionally integrate an automatic shutdown circuit thatmay terminate all electrical functions of the snowmobile 10 in case ofsystem failure.

Table I provides a sequence of events including a manual start procedureof the ICE 24, followed by an electric start procedure command receivedafter a waiting time that does not exceed the capabilities of theelectric start system. In Table I, mentions of “PWM” refer to “pulsewidth modulation”, a technique that may optionally be used in the firstand second control strategies to control delivery of electric powerbetween the capacitance 145 and the motor-generator 144, as expressedhereinbelow.

TABLE I Motor- ECU 164 Capacitance Q1 and Q2 generator TYPE Event stateC1 voltage 145 voltage states 144 MANUAL Initial OFF 0 volt 0 volt Q1off; Stopped conditions Q2 off Pulling Wake-Up Rising 0 volt Q1 off;Rising the rope Q2 off speed (1^(st) time) Pulling Firing Rising to 0volt Q1 off; Rising to the rope nominal Q2 off idle speed (2^(nd) time)voltage Releasing Ignition/ Nominal Rising, but less Q1 100% on; Idlespeed the rope PWM voltage than nominal Q2 off or engine voltage running— Stop Turning Falling Nominal Q1 off; Falling OFF voltage Q2 off speedWaiting OFF Close to 0 Less than Q1 off; Stopped time volt nominal Q2off voltage, but equal to or above V_(MinE) ELECTRIC Electric Wake-UpClose to 0 Less than Q1 off; Stopped start volt nominal Q2 off commandvoltage, but equal to or above V_(MinE) — Ignition/ Equalizing toReducing Q1 on for a Stopped PWM the slightly short period, capacitancethen off; voltage Q2 initially off, then cycling on and off — CrankingEqual to the Reducing, but Q1 off; Rising capacitance still equal to orQ2 100% on speed voltage above V_(MinR) — Firing Rising Rising Q1 off;Rising to Q2 100% on idle speed Ready to Ignition/ Nominal Nominal Q1100% on; Idle speed apply PWM voltage voltage Q2 off or engine throttlerunning

In Table I, the expression “idle speed or engine running” means that theICE 24 is started and running on its own, no torque being appliedthereon by the motor-generator 144 or by use of the recoil starter 156.

In at least one implementation, both minimum voltage thresholds V_(MinE)and V_(MinR) may be defined within an operating voltage range of thedirect fuel injectors 132 a and 132 b so that, if the voltage of thecapacitance 145 is not sufficient for the direct fuel injectors 132 aand 132 b to inject fuel in the cylinders 106A, 106B, the electric startprocedure is not attempted, or terminated if unsuccessful.

Electric Start Procedure

FIG. 9 is a logic diagram of a method for starting the engine of FIG. 2according to an implementation. A sequence shown in FIG. 9 comprises aplurality of operations, some of which may be executed in variableorder, some of the operations possibly being executed concurrently, andsome of the operations being optional. The method begins at operation300 when the ICE 24 of the snowmobile 10 is stopped. A voltage of thecapacitance 145 is measured by the voltage sensor 167 at operation 302.In the same operation 302, the display 186 may provide an “automaticstart” indication if the voltage meets or exceeds the electric startvoltage threshold V_(MinE) and if other conditions described hereinbelowfor the electric start procedure are met. The user actuates the electricstart switch 168, this being detected by the start command detector 212at operation 304. At operation 322, in response to the detection of theelectric start request, the ECU 164 controls the drivers 216 and 217 ofthe transistors Q1 and Q2 to allow the capacitance 145 to charge thecapacitor C1 until their voltages are equalized. The ECU 164 and thevarious sensors, including in particular the ACPS 170, are energized bythe capacitance 145 as a result of this voltage equalization. Acomparison is then made by the ECU 164, at operation 306, between thevoltage of the capacitance 145 and the electric start voltage thresholdV_(MinE) to determine whether it is possible to initiate the electricstart procedure for the ICE 24. If it is determined that the voltage ofthe capacitance 145 is below the electric start voltage thresholdV_(MinE), the electric start procedure is prevented. Otherwise,verification is made at operation 308 that the engine temperaturemeasured by the engine temperature sensor 172 meets or exceeds an enginetemperature threshold Th0. The electric start procedure is prevented inthis threshold for the engine temperature is not met. Otherwise,verification is made at operation 310 that the ECU temperature sensor182 provides a reading of the temperature of the ECU 164 that meets orexceeds an ECU temperature threshold Th1. The electric start procedureis prevented if this threshold for the ECU temperature is not met.Additional operations related to use of measurements obtained from othersensors introduced in the foregoing description of FIG. 6 may takeplace. These measurements may be provided to the ECU 164 by the airtemperature sensor 174, the atmospheric temperature sensor 176, or thetimer 180. Additional tests based on those measurements may be executedby the ECU 164 to determine whether or not the electric start procedureis likely to succeed or to determine a torque value sufficient to causethe rotation of the crankshaft 100. For example, the electric startprocedure may be made conditional, in the ECU 164, on the timer 180informing the ECU 164 that a period of time since the ICE 24 has beenstopped is below a predetermined time value when the user actuates theelectric start switch 168 at operation 304. On the basis of the periodof time since the ICE 24 has been stopped, it is possible to estimatewhether the voltage of the capacitance 145 will have fallen below theelectric start voltage threshold V_(MinE) knowing a maximum chargevoltage of the capacitance 145 from a previous running sequence of theICE 24, and based on a typical energy leakage of the capacitance 145.

Whether the electric start procedure is prevented because the voltage ofthe capacitance 145 is insufficient (operation 306), because the enginetemperature is too low (operation 308), because the ECU temperature istoo low (operation 310), or for any other reason, the method proceeds tooperation 312. At operation 312, the ECU 164 causes the display 186 todisplay “Manual Start” or some other message indicating to the user ofthe snowmobile 10 that the snowmobile 10 will need to be startedmanually using the recoil starter 156 (i.e. by pulling on the handle163). In implementations where the assisted start procedure isavailable, the display 186 may instead display “Assisted Start” or someother equivalent message, provided that current conditions allow usingthis procedure. Displaying the manual start indication or the assistedstart indication at operation 312 may follow any decision taken by theECU 164 to not proceed with the electric start procedure. It iscontemplated that instead of providing a message on the display 186,that the ECU 164 could cause a sound to be heard or provide some othertype of feedback to the user of the snowmobile 10, indicating that thesnowmobile 10 will need to be started manually using the recoil starter156. A manual start procedure or an assisted start procedure may beinitiated when the user pulls on the rope 158 of the recoil starter 156.If conditions for the assisted start procedure are met, this proceduremay be initiated as described hereinbelow. Otherwise, when theconditions for the assisted start procedure are not met, the manualstart procedure may be initiated at operation 314 when, in response tosensing the operation of the recoil starter 156 by the user of thesnowmobile 10, the ECU 164 initiates an engine control procedureassociated with the use of the recoil starter 156 in order to start theICE 24 using the recoil starter 156. Then at operation 316, the ECU 164determines if the ICE 24 has been successfully started using the recoilstarter 156. If not, then operation 314 is repeated. It is alsocontemplated that if at operation 316 it is determined that the ICE 24has not been successfully started, that the method could return tooperation 312 to display the message again. If at operation 316 it isdetermined that the ICE 24 has been successfully started, then themethod proceeds to operations 318 and 320, these last two (2) operationsbeing operated concurrently. At operation 318, the ECU 164 operates theICE 24 according to the control strategy or strategies to be used oncethe ICE 24 has started. At operation 320, the ECU 164 controls theinverter 146 to cause power to be delivered from the motor-generator 144to the capacitance 145, charging the capacitance 145 using the secondcontrol strategy at a voltage that remains fairly constant for a widerange of rotational speeds of the crankshaft 100. This may be achievedby the ECU 164 shunting one or more of the Phases A, B and C of themotor-generator 144 if, in the second control strategy, themotor-generator 144 generates a voltage that exceeds a maximum voltagethreshold. The ECU 164 may linearly regulate the voltage generated bythe motor-generator 144 by using a series regulation mode or a shuntmode. The maximum voltage threshold may for example be equal or slightlysuperior to the nominal voltage of the circuit 200.

If at operations 306, 308 and 310 the ECU 164 determines that thecapacitance voltage is equal to or above the electric start voltagethreshold V_(MinE) and that the temperature conditions and any othercondition are also met, the method continues at operation 324 where theECU 164 obtains a value of the absolute angular position of thecrankshaft 100 from the ACPS 170. This operation 324 may continue on anongoing fashion during the complete electric start procedure so that thefollowing operations may be optimized according to the varying angularposition of the crankshaft 100. It is contemplated that operations 322and 324 may be omitted or substituted with other actions. For example,the electric start procedure may be rendered independent from theangular position of the crankshaft 100 by providing a capacitance 145,the battery, or other power source having sufficient energy storagecapability to rotate the crankshaft 100 with no concern for its actualangular position.

The electric start procedure proceeds with operation 326 and continuesthrough operations 328, 330 and, if required, operation 332. Theseoperations are initiated in the sequence as shown on FIG. 9, but arethen executed concurrently until the electric start procedure is foundsuccessful or until it needs to be terminated.

At operation 326, the ECU 164 determines the torque value sufficient tocause the rotation of the crankshaft 100 and initiates delivery of powerfrom the capacitance 145 to the motor-generator 144, through theinverter 146, via the first control strategy which adapts the deliveryof power in view of the determined torque value. This transfer of powercauses a rotation of the crankshaft 100. Optionally, the ECU 164 maydetermine the torque value in sub-steps, in which a first sub-stepcomprises delivering electric power from the capacitance 145 to thethree-phase motor-generator 144 according to a first torque value tocause slow turning of the crankshaft at a first rotational speed untilthe piston is brought beyond its top dead center (TDC), based oninformation provided by the ACPS 170 and based on the contents of thecontrol maps 166, a second sub-step comprising delivering electric powerfrom the capacitance 145 to the three-phase motor-generator 144according to a second torque value, greater than the first torque valueto cause turning of the crankshaft at a second rotational speed, thesecond rotational speed being greater than the first rotational speed.

While operation 326 is ongoing, particularly while the second sub-stepis ongoing if operation 326 comprises two sub-steps, the method proceedsto operation 328 in which the ECU 164 causes the direct fuel injectors132 a, 132 b to inject fuel directly in the combustion chambers 120 a,120 b and causes the spark plugs 134 a, 134 b to ignite the fuel in thecombustion chambers 120 a, 120 b, thereby accelerating the rotation ofthe crankshaft 100. The absolute angular position of the crankshaft 100may be used by the ECU 164 to properly time the fuel injection and theignition. The ACPS 170 being an absolute position sensor, it candetermine the position of the crankshaft 100 while it is stationary,prior to starting of the ICE 140. This technique provides precise fuelinjection and ignition timing at a very low rotational speed of the ICE24, such as when the ICE 24 is starting. This technique decreases thechances of a failed start procedure due to an insufficient combustionwithin the combustion chambers 102A, 120B, this insufficient combustionresulting from imprecise fuel injection quantities or ignition timingcalculated from an imprecise crankshaft position. This technique furtherpromotes faster synchronization between all components of the ICE 24that rely on the position of the crankshaft 100 when compared to the useof position sensors that require the crankshaft 100 to be rotating todetermine its position. Use of mechanical actuators (not shown) operablyconnected to the crankshaft 100 to control injection and ignitiontimings is also contemplated. It is further contemplated that a quantityof fuel to be injected and the ignition timing as applied by the ECU 164at operation 328 may be evaluated using any known method, optionallydepending on one or more of an engine temperature, an air temperature,an atmospheric pressure, and an exhaust temperature, these values beingprovided to the ECU 164 by the various sensors shown on FIG. 6.

While operations 326 and 328 are ongoing, the method proceeds tooperation 330, in which the ECU 164 compares a rotational speed of thecrankshaft 100 to a minimum revolution threshold to determine if the ICE24 has been successfully started using the electric start procedure. Ifthe rotational speed of the crankshaft 100 is equal to or above theminimum revolution threshold, the ICE 24 has been successfully started,the electric start procedure ends and the method proceeds to operations318 and 320, which are described hereinabove.

If, at operation 330, the ECU 164 determines that the ICE 24 has not yetbeen started, the rotational speed of the crankshaft 100 being below theminimum revolution threshold, the method continues at operation 332where the ECU 164 monitors again the voltage of the capacitance 145. Itis expected that this voltage will be reduced somewhat as energypreviously stored in the capacitance 145 has been spent duringoperations 326 and 328. However, if a remaining voltage of thecapacitance 145 is equal to or above the residual voltage thresholdV_(MinR), the electric start procedure returns to operations 326 and328, which are still ongoing, and then at operation 330. If however theECU 164 determines at operation 332 that the capacitance voltage hasfallen below the residual voltage threshold V_(MinR), the methodproceeds to operation 334 where the ECU 164 ceases the delivery of powerfrom the capacitance 145 to the motor-generator 144 and terminatesoperations 326 and 328. The method then moves from operation 334 tooperation 312, which is described hereinabove, in which the ECU 164causes the display 186 to display a manual start indication, or anassisted start indication in implementations where this option isavailable, operation 312 being followed by operations 314, 316, 318 and320 in the case of a manual start.

FIG. 10 is a timing diagram showing an example of variations of anengine resistive torque as a function of time along with correspondingengine rotational speed variations. A graph 400 shows a variation of theresistive torque of the ICE 24, in Newton-Meters (Nm) as a function oftime, in seconds. The graph 400 was obtained from a Simulink™ model. Asshown on the graph 400, the rotational speed in the starting phase isabout 100 revolutions per minute (RPM). The resistive torque may vary inrelation to the rotational speed of the crankshaft 100. A graph 402shows a corresponding variation of a rotational speed of the crankshaft100 over the same time scale. In the simulation, the two-cylinder ICE 24is firing when a piston first reaches near TDC. After less than 0.1seconds, the resistive torque becomes negative because the piston haspassed beyond its TDC. Compression present in the combustion chamberpushes on the piston and accelerates the rotation of the crankshaft 100.At about 0.12 seconds, the ECU 164 controls the torque applied to thecrankshaft 100 by the motor-generator 144, accelerating the rotation ofthe crankshaft 100. The rotational speed of the crankshaft 100 reaches aplateau at about 0.17 seconds because the piston is now compressinggases that may remain present in the combustion chamber. The rotationalspeed decreases as the piston arrives near its TDC. TDC is reached atabout 0.32 seconds. Successful ignition takes place, whereafter therotational speed of the crankshaft 100 increases rapidly while theresistive torque on the motor-generator 144 becomes essentiallynegative, following a toothed saw wave shape as the piston cycles up anddown in its cylinder.

Assisted Start Procedure

FIG. 11 is a logic diagram of a method for starting the engine of FIG. 2according to another implementation. A sequence shown in FIG. 11comprises a plurality of operations, some of which may be executed invariable order, some of the operations possibly being executedconcurrently, and some of the operations being optional. The methodbegins at operation 600 when the ICE 24 of the snowmobile 10 is stopped.A voltage of the capacitance 145 is measured by the voltage sensor 167at operation 602. In the same operation 602, the display 186 may providean “assisted start” indication if the voltage meets or exceeds theassisted start voltage threshold V_(MinA) and if other conditionsdescribed hereinbelow for the assisted start procedure are met. Atoperation 604, the user initiates a rotation of the crankshaft 100 bypulling on the rope 158 of the recoil starter 156, this operation beingdetected by the CPS 171 that in turn sends the initiating signal to thestart command detector 212 to wake up the ECU 164. In one variant, theACPS 170 becomes energized at the onset of the start procedure by theECU 170 which has itself been awaken by the CPS 171. In another variant,the ACPS 170 is permanently connected to the capacitance 145 so that itis able to detect the absolute angular position of the crankshaft 100whenever the capacitance 145 holds at least a minimum charge. Detectingthe initial rotation of the crankshaft 100 may be conditional to theACPS 170 detecting that a revolution speed of the crankshaft 100 meetsor exceeds a minimal revolution threshold. At operation 606, the ECU 164controls the drivers 216 and 217 of the transistors Q1 and Q2 to allowthe capacitance 145 to charge the capacitor C1 until their voltages areequalized. The ECU 164 and the various sensors, including in particularthe ACPS 170, are energized by the capacitance 145 as a result of thisvoltage equalization. A comparison is made by the ECU 164 at operation608 between the voltage of the capacitance 145 and the assisted startvoltage threshold V_(MinA) to determine whether it is possible toinitiate the assisted start procedure for the ICE 24. If it isdetermined that the voltage of the capacitance 145 is below the assistedstart voltage threshold V_(MinA), the assisted start procedure isprevented. Otherwise, verification is made at operation 610 that theengine temperature measured by the engine temperature sensor 172 meetsor exceeds an engine temperature threshold ThO. The assisted startprocedure is prevented in this threshold for the engine temperature isnot met. Otherwise, verification is made at operation 612 that the ECUtemperature sensor 182 provides a reading of the temperature of the ECU164 that meets or exceeds an ECU temperature threshold Th1. The assistedstart procedure is prevented if this threshold for the ECU temperatureis not met. Additional operations related to the use of measurementsobtained from other sensors introduced in the foregoing description ofFIG. 6 may take place. These measurements may be provided to the ECU 164by the air temperature sensor 174, the atmospheric temperature sensor176, or the timer 180. Additional tests based on those measurements maybe executed by the ECU 164 to determine whether or not the assistedstart procedure is likely to succeed. For example, the assisted startprocedure may be made conditional, in the ECU 164, on the timer 180informing the ECU 164 that a period of time since the ICE 24 has beenstopped is below a predetermined time value when the user pulls on therope 158 of the recoil starter 156 at operation 604. On the basis of theperiod of time since the ICE 24 has been stopped, it is possible toestimate whether the voltage of the capacitance 145 will have fallenbelow the assisted start voltage threshold V_(MinA) knowing a maximumcharge voltage of the capacitance 145 from a previous running sequenceof the ICE 24, and based on a typical energy leakage of the capacitance145.

Displaying the manual start indication at operation 614 may follow anydecision taken by the ECU 164 to not proceed with the assisted startprocedure. Whether the assisted start procedure is prevented because thevoltage of the capacitance 145 is insufficient (operation 608), becausethe engine temperature is too low (operation 610), because the ECUtemperature is too low (operation 612) or for any other reason, themethod proceeds to operation 614. At operation 614, the display 186 maydisplay “Manual Start”. Following operation 614, the user may continuepulling on the rope 158 of the recoil starter 156 at operation 616.Operation 616 may continue until it is detected at operation 618 thatthe ICE 24 is properly started. Control of ICE 24 and delivery ofelectric power from the motor-generator 145 to the capacitance 144follow at 620 and 622, which are the same or equivalent as operations318 and 320 of FIG. 9 including, in an implementation, controlling theICE 24 using the above described control strategies.

If at operations 608, 610 and 612, the ECU 164 determines that thecapacitance voltage is equal to or above the assisted start voltagethreshold V_(MinA) and that the temperature conditions and any furthercondition are also met, the method continues at operation 624 where theACPS 170 senses a current, absolute angular position of the crankshaft100.

The assisted start procedure proceeds with operation 626 and continuesthrough operations 628, 630 and, if required, operation 632. Theseoperations are initiated in the sequence as shown on FIG. 11, but arethen executed concurrently until the assisted start procedure is foundsuccessful or until it needs to be terminated.

At operation 626, the ECU 164 initiates delivery of power from thecapacitance 145 to the motor-generator 144, through the inverter 146.This transfer of power accelerates the rotation of the crankshaft 100and reduces the amount of effort that needs to be exerted by the userpulling on the rope 158 of the recoil starter 156. The ECU 164 mayoptionally determine a torque value in the same manner as described inthe foregoing description of operation 326 (FIG. 9).

While operation 626 is ongoing, the method proceeds to operation 628 inwhich the ECU 164 causes the direct fuel injectors 132 a, 132 b toinject fuel directly in the combustion chambers 120 a, 120 b and causesthe spark plugs 134 a, 134 b to ignite the fuel in the combustionchambers 120 a, 120 b, thereby accelerating further the rotation of thecrankshaft 100. The angular position of the crankshaft 100 is used bythe ECU 164 to properly time the fuel injection and the ignition. It iscontemplated that a quantity of fuel to be injected and the ignitiontiming as applied by the ECU 164 at operation 628 may depend on one ormore of an engine temperature, an air temperature, an atmosphericpressure, and an exhaust temperature, these values being provided to theECU 164 by the various sensors shown on FIG. 6.

While 626 and 628 are ongoing, the method proceeds to operation 630, inwhich the ECU 164 compares a rotational speed of the crankshaft 100 to aminimum revolution threshold to determine if the ICE 24 has beensuccessfully started using the assisted start procedure. If therotational speed of the crankshaft 100 is equal to or above the minimumrevolution threshold, the ICE 24 has been successfully started, theassisted start procedure ends and the method proceeds to 620 and 622,which are described hereinabove.

If, at operation 630, the ECU 164 determines that the ICE 24 has not yetbeen started, the rotational speed of the crankshaft 100 being below theminimum revolution threshold, the method continues at operation 632where the ECU 164 monitors again the voltage of the capacitance 145. Itis expected that this voltage will be reduced somewhat as energypreviously stored in the capacitance 145 has been spent during 626 and628. However, if a remaining voltage of the capacitance 145 is equal toor above a residual voltage threshold, the assisted start procedurereturns to operations 626 and 628, which are still ongoing, and then atoperation 630. In one variant, the residual voltage threshold applicableto the assisted start procedure may be the same value V_(MinR) as in thecase of the electric start procedure. In another variant, a differentresidual voltage threshold may be used given that the amount of powerdelivered to the motor-generator 144 by the capacitance 145 complementsthe effort of the user pulling on the rope 158 of the recoil starter156. If however the ECU 164 determines at operation 632 that thecapacitance voltage has fallen below the residual voltage thresholdV_(MinR), the method proceeds to operation 634 where the ECU 164 ceasesthe delivery of power from the capacitance 145 to the motor-generator144 and terminates operations 626 and 628. The method then moves fromoperation 634 to operation 614, which is described hereinabove, in whichthe ECU 164 causes the display 186 to display a manual start indication,operation 614 being followed by operations 616, 618, 620 and 622.

In an implementation, the snowmobile 10 may be configured to support anyone of the manual, electric and assisted start procedures. In suchimplementation, operation 312 (FIG. 9) may provide a manual start or anassisted start indication, depending on the voltage of the capacitance145. If the voltage of the capacitance is below the electric startvoltage threshold V_(MinE) while meeting or exceeding the assisted startvoltage threshold V_(MinA), operation 312 of FIG. 9 may provide theassisted start indication and may be followed by operation 604 of FIG.11 if the user pulls on the rope 158 of the recoil starter 156. Also inthis implementation, after having started the ICE 24 using the assistedstart procedure, the ICE 24 may be stopped and the display 186 mayprovide an indication of the available start procedure depending oncurrent conditions reported to the ECU 164 by the various sensors.

Implementations of the Control Strategies

As expressed hereinabove, the ECU 164 controls the inverter 146 throughthe strategy switch 184. To this end, the ECU 164 generates controlpulses that are applied to the strategy switch 184. These control pulsesare generated differently in the two (2) control strategies. In at leastone implementation, the effect of these control pulses depends on theinternal structure of the inverter 144. FIG. 12 is a circuit diagramshowing connections of the inverter 146, the capacitance 145 and themotor-generator 144 of FIG. 6. As shown on FIG. 12, the inverter 146 hasthree phases, each phase being electrically connected to a correspondingphase of the three-phase motor-generator 144. In more details, theinverter 146 is formed of three (3) switching legs, each switching legincluding a pair of MOSFETs T1, T2, T3, T4, T5 and T6 matched withcorresponding freewheel diodes D2, D1, D3, D2, D6 and D5. For instance,a first leg forming a first phase includes a top transistor T1 matchedwith a freewheel diode D2 and a bottom transistor T2 matched with afreewheel diode D1. A second leg forming a second phase includestransistors T3 and T4 matched with diodes D4 and D3 respectively while athird leg forming a third phase includes transistors T5 and T6 matchedwith diodes D6 and D5 respectively. As substitutes to MOSFETs, bipolartransistors, for example IGBTs, or any other power electronic switchesare also contemplated. Each transistor T1-T6 has a corresponding gateG1-G6 through which a signal, or control pulse, can be applied under thecontrol of the ECU 164 via the strategy switch 184, either directly orthrough a gate driver (not shown), to turn-on (short-circuit) orturn-off (open circuit) the corresponding transistors T1-T6. Thefreewheel diodes D1-D6 are used to attenuate transient overvoltage thatoccurs upon switching on and off of the transistors T1-T6.

For example, when the motor-generator 144 is in motor operating mode,being used as a starter for the ICE 24, a first control pulse is appliedat the gate G1 to short-circuit the transistor T1. Current flows from apositive tab of the capacitance 145 through the transistor T1 andreaches a phase of the motor-generator 144 defined between an input Aand a neutral connection between the phases of the motor-generator 144,hereinafter “Phase A”. Thereafter, the first control pulse is removedfrom the gate G1 so the transistor T1 becomes an open-circuit. At thesame time, a second control pulse is applied on the gate G2, causing thetransistor T2 to turn-on. Current now flows in the opposite direction inPhase A of the motor-generator 144, returning to a negative tab of thecapacitance 145 via the transistor T2. As a result of this sequence ofturning on and off the transistors T1 and T2, an alternating currentflows in the Phase A of the motor-generator 144.

The current flowing into Phase A of the motor-generator 144 needs toexit through one or both of the other phases of the motor-generator 144.“Phase B” is defined between an input B and the neutral connection.“Phase C” is defined between an input C and the neutral connection. Thecurrent flows from Phase A through Phase B, or Phase C, or both Phases Band C, depending on whether one or both of transistors T4 or T6 isturned on by control pulses applied on their respective gates G4 or G6when the transistor T1 is also turned on. The current exiting themotor-generator 144 via one or both of Phases B and/or C returns to anegative tab of the capacitance 145 through one or both of thetransistors T4 and/or T6. The freewheel diodes D1-D6 assist insupporting phase inductance currents during freewheel periods.

To operate the motor-generator 144 as a conventional three-phase motor,current would flow concurrently in all three (3) Phases A, B and C, atiming control of the various transistors T1-T6 being separated by 120degrees. Other operating modes of the motor-generator 144 in whichcurrent does not concurrently flow in all three (3) Phases A, B and Care however contemplated.

Examples of parameters that may be considered by programming of the ECU164 to control the delivery of electric power in both control strategiesinclude, without limitation, current and voltage of each phase voltagesand currents in each of the Phases A, B and C of the motor-generator144, the angular position and rotational speed of the crankshaft 100.The ECU 164 uses these values to determine an electromagnetic torque ofthe motor-generator 144, this torque having positive value when themotor-generator 144 is used during the electric start procedure or theassisted start procedure and a negative value when used in generatoroperating mode.

The first control strategy uses a technique called vector control.Suitable examples of vector control techniques include field-orientedcontrol (FOC), direct-torque control (DTC), direct self-control (DSC),space vector modulation (SVM), and the like. Use of any one of suitablevector control techniques is contemplated and within the scope of thepresent disclosure. The first control strategy is used mainly to controlthe delivery of electric power from the capacitance 145 to themotor-generator 144 to cause or assist a rotation of the crankshaft 100in the electric start procedure or in the assisted start procedure ofthe ICE 24. In one implementation, ECU 164 determines a torque requestsufficient to cause the rotation of the crankshaft 100. In anotherimplementation, the ECU 164 determines a speed request applicable to thecrankshaft 100, sufficient to cause ignition and start of the ICE 24.This determination of the speed request or torque request may be made bythe ECU 164 applying a predetermined speed or torque request value orpattern based on the contents of the control maps 166. The ECU 164 mayincrement the torque request if a first torque application causes norotation of the crankshaft 100. The ECU 164 may increment the speedrequest if a rotation of the crankshaft 100 is not sufficient to allowignition and start of the ICE 24. Alternatively, the ECU 164 maycalculate the speed or torque request based on a combination ofparameters, including in a non-limitative example a mathematicalrepresentation of internal components of the ICE 24 and on the absoluteangular position of the crankshaft 100. The ECU 164 controls thedelivery of electric power from the capacitance 145 to themotor-generator 144, based on the determined speed request or torquerequest, through the generation of control pulses applied to selectedones of the transistors T1-T6. Using vector control, the ECU 164calculates a number, timing, and width of the various control pulses sothat the amount of electric power flowing from the capacitance 145through the inverter 146 and to the motor-generator 144 fulfills thedetermined speed or torque request. This manner of controlling thetransistors T1-T6 by applying timed pulses to their gates G1-G6, eachpulse having a calculated width, is known as pulse width modulation(PWM).

FIG. 13 is a block diagram of a typical implementation of a vectorcontrol drive. A vector control drive 500 of FIG. 13 may be implementedat least in part in the ECU 164. An input to the vector control driveincludes a set point 504 for a required speed (the speed request) thatis determined as sufficient for starting the ICE 24. This set point 504is applied to a slow speed control loop 506. Other inputs to the vectorcontrol drive 500 include current measurements 508 _(a), 508 _(b) and508 _(c) for the three phases of the motor-generator 144 and a voltagemeasurement 510 obtained from the inverter 146 and/or from themotor-generator 144. These current and voltage measurements are appliedto an analog to digital converter (ADC) 512. Crankshaft angular positionmeasurements (encoder signals u_(A), u_(S)) 514 that are obtained fromthe ACPS 170 are applied to a quadrature timer 516. Because themotor-generator 144 is mounted coaxially to the crankshaft 100, theencoder signals u_(A), u_(S) 514 also represent the actual angularposition of the rotor 150 of the motor-generator 144. The vector controldrive 500 uses this information to calculate a torque request, asexplained in the following paragraphs. The quadrature timer 516calculates an actual position of the crankshaft 100. The ADC 512calculates a digitized voltage value 518 and digitized current values520 _(a), 520 _(b) and 520 _(c) for the three phases of themotor-generator 144. These digitized values and an actual position 522of the crankshaft 100 calculated by the quadrature timer 516 areprovided to a fast current control loop 524. The actual position 522 ofthe crankshaft 100 is converted to an actual (measured) speed 526 by aspeed calculator 528 of the slow speed control loop 506. A difference528 between the measured speed 526 and the required speed set point 504is applied to a first proportional-integral (PI) controller 530 that inturn yields a current-image 532 of a torque request that is applied as aset point (Isq_req) to the fast current control loop 524.

As expressed hereinabove, in some variants, it may be desired to operatethe motor-generator 144 so that it delivers electric power to thecapacitance 145 in the first control strategy, at least at lowrevolution speeds of the crankshaft 100. To this end, an optional fieldweakening module 534 having an internal map attenuates values of itsoutput based on the measured speed 526 of the crankshaft 100 to providea current-image 536 of a magnetic field of the motor-generator 144 as anadditional set point (Isd_req) applied to the fast current control loop524.

In the fast current control loop 524, a Clark Transform 538 converts thethree-phase current measurements 520 _(a), 520 _(b) and 520 _(c) into atwo-phase model 540. A Park Transform 542 fed with sine and cosinevalues 523 of the actual position 522 of the crankshaft 100, calculatedby a sin/cos converter 525, converts further this model 540 to provide astationary current-image 544 of the actual torque on the motor-generator144 (Isq) and a stationary current-image 546 of the actual magneticfield of the motor-generator (Isd). Outputs 544 and 546 of this modelare respectively compared to the Isq_req set point 532 and to theIsd_req set point 536 (if used), and their differences are respectivelyapplied to second and third PI controllers 548, 550. An Inverse ParkTransform 552 is applied to stationary voltage requests Uq 554 and Ud556 produced by the second and third PI controllers 548, 550, theInverse Park Transform 552 using the sine and cosine values 523 of theactual position 522 of the crankshaft 100 to produce outputs 558, 560 ofthe Inverse Park Transform 552 that are applied to a space vectormodulation-pulse width modulation (SV-PWM) transform 562. In turn, theSV-PWM transform 562 provides three-phase control 564 to a PWM module566 that generates pulses 502 that the ECU 164 provides for applicationto the gates G1-G6 of the inverter 146.

The ECU 164 may control a delivery of electric power from thecapacitance 145 to the motor-generator 144 based on a pre-determinedamount of torque, or torque request, sufficient to cause rotation of thecrankshaft 100 for starting the ICE 24. However, considering that theamount of torque required to rotate the crankshaft 100 before ignitionof the cylinder (or cylinders) varies based on the angular position ofthe crankshaft 100 in relation to the top dead center (TDC) position ofeach piston, calculation of a variable torque request is alsocontemplated. The absolute angular position of the crankshaft 100 isprovided by the ACPS 170. In a variant introduced in the foregoingdescription of operation 326 (FIG. 9), the ECU 164 calculates orotherwise determines the torque request based on the absolute angularposition of the crankshaft 100 provided by the ACPS 170, values of thetorque request being updated at various points of the rotation of thecrankshaft 100. As a result, the torque request can be optimized so thatit is sufficient to rotate the crankshaft 100 as it reaches variousangular positions while using as little as possible of the energy storedin the capacitance 145. In a particular variant, the ECU 164 controlsthe amount of torque applied on the motor-generator 144 so that it turnsat a very low speed until a given piston 116A, 116B passes its TDC for afirst time. During this brief period of time, gas is slowly expelledfrom the combustion chamber 120A, 120B in which this given piston 116A,116B is located. Very little energy is drawn from the capacitance 145 inthis operation. Once the piston 116A, 116B has moved beyond its TDC, thecrankshaft 100 has acquired at least some momentum. The ECU 164 thenraises the torque request applied to the motor-generator 144 so that thecrankshaft 100 rotates at a speed sufficient to allow injection of fuelin the combustion chamber 120A, 120B as the piston 116A, 116B movestowards its TDC, ignition taking place in the combustion chamber 120A,120B as soon as the piston moves beyond its TDC. This increase of thetorque request may be linear until a predetermined torque set-point isreached, so that the rotational speed of the crankshaft 100 increasessmoothly.

Following starting of the ICE 24, irrespective of whether the ICE 24 wasstarted using the manual start procedure, the assisted start procedureor the electric start procedure, the crankshaft 100 drives themotor-generator 144 at a variable rotational speed, most of the timesignificantly exceeding a rotational speed used in the course of any ofthe start procedures. Once the ICE 24 is started, operation of themotor-generator 144 switches to generator operating mode. In animplementation, the ECU 164 may determine a revolution speed of thecrankshaft 100 based on successive readings provided by the CPS 171 orthe ACPS 170 and cause the motor-generator 144 to start deliveringelectric power to the capacitance 145 when the revolution speed of thecrankshaft meets or exceeds a minimal revolution threshold. At thispoint or soon thereafter, the ECU 164 starts controlling the strategyswitch 184 and the inverter 146 using the second control strategy.Optionally, the first control strategy may be used in generatoroperating mode until the voltage measurement provided by the voltagesensor 167 meets or exceeds a voltage generation threshold. The voltagegeneration threshold can be set slightly lower than a nominal voltage ofthe capacitance 145, for example.

The second control strategy uses a “shunt” technique. The output of themotor-generator 144, now generating, is used to charge the capacitance145, to supply electrical power to the direct fuel injectors 132 a, 132b, to spark the spark plugs 134 a, 134 b, and, generally, to supplyelectrical power to electrical accessories of the snowmobile 10. To thisend, the ECU 164 alters a position of the strategy switch 184 so thatelectrical power now flows from the motor-generator 144 to thecapacitance 145, still through the inverter 146. The ECU 164 monitorsthe voltage of the capacitance 145 through measurements obtained fromthe voltage sensor 167. Based on these voltage measurements, the ECU 164generates control pulses that are applied, via the strategy switch 184,to the gates G1-G6 of the transistors T1-T6 in the inverter 146. PWM isstill applied by the ECU 164 to the gates G1-G6, but this time accordingto the second control strategy.

If an output voltage of the motor-generator 144 is above its nominalvalue, or above its nominal value plus a predetermined tolerance factor,the inverter 146 is controlled by the ECU 164 to reduce the voltage atwhich electrical power is delivered from the motor-generator 144 to thecapacitance 145. To this end, in one operating mode called dissipativevoltage regulation mode, the ECU 164 may generate control pulses appliedto various gates G2, G4 and G6 to effectively bypass, or “shunt”, one ormore of the phases of the motor-generator 144, at the same time applyingno control pulse to the gates G1, G3 and G5 in order to cause thetransistors T1, T3 and T5 to remain non-conductive (open circuit). Forexample, applying pulses to the gates G2 and G6 causes the transistorsT2 and T6 to turn on and become conductive. As a result, a closed loopis formed between Phases A and C of the motor-generator 144 along withthe transistors T2 and T6. Under this condition, no electrical power isdelivered from two (2) of the phases of the motor-generator 144 to thecapacitance 145. A duration (width) and timing of the pulses applied tothe gates G2 and G6 impacts a duration of time when Phases A and C areshunted, in turn impacting the charging voltage applied at thecapacitance 145. PWM can be applied to any pair of the bottomtransistors T2, T4 and T6, so that they can be shorted at a desired timeto shunt a pair of phases of the motor-generator 144. The ECU 164 mayactually modify, over time, a determination of which pair of transistorsis made part of a shunt in order to avoid their overheating due toconduction losses in the inverter 146. To this end, voltage regulationin shunt mode involves successively activating the transistors T2, T4and T6. As a result, the delivery of electric power from themotor-generator 144 to the capacitance 145 can be made at a desiredvoltage over a broad range of the rotational speed of the crankshaft100. A series voltage regulation mode is also contemplated, in which thefreewheel diodes D1, D3 and D5 may optionally be replaced by additionaltransistors (not shown) mounted in reverse-parallel with the transistorsT1, T3 and T5, these additional transistors being turned on and off asrequired to allow current from the motor-generator 144 to recharge thecapacitance 145 while not exceeding the nominal voltage value.

In a particular implementation, voltage regulation in shunt mode maybenefit from the measurements provided by the CPS 171 or the ACPS 170.In this implementation, the CPS 171 or the ACPS 170 allows the ECU 164to determine a mechanical position of the crankshaft 100. The ECU 164calculates an equivalent electrical angle by multiplying the mechanicalposition of the crankshaft 100 by a known number of pole pairs of themotor-generator 144. If the output voltage of the motor-generator 144 isabove a predetermined value, starting from a voltage rise of any one ofthe phases A, B or C, all three (3) phases are consecutively shuntedonce, in synchrony with the operation of the motor-generator 144. Thisshunting sequence may be repeated when the output voltage of themotor-generator 144 rises again above the predetermined value.

If the voltage of the capacitance 145 is at or below its nominal value,the inverter 146 is controlled by the ECU 164 to deliver electricalpower available from the motor-generator 144 to the capacitance 145without shunting any of the Phases A, B or C. Under this condition,which may for example occur for a brief duration after the start of theICE 24, the control of the power delivery could be construed as aneutral control mode distinct from the first and second controlstrategies. In the neutral control mode, the inverter146 acts as athree-phase full-wave diode bridge rectifier, providing no voltage orcurrent regulation.

FIG. 14 is a block diagram of an electric system according to animplementation of the present technology. A circuit 700 includesvariants of elements introduced in the foregoing description of thevarious drawings, these elements being grouped into subsystems. Themotor-generator 144 is one such subsystem. Another subsystem is in theform of a control module 702 that, in an implementation, comprises asingle physical module including a processor 703 programmed to executethe functions of the ECU 164, the inverter 146, the ECU temperaturesensor 182 and further includes a DC-DC converter 704. As shown, the ECU164 includes connections for the electric start switch 168, for themeasurements provided by the various sensors 167, 170, 171, 172, 174,176 and 182, and connections to the gates G1-G6 of the inverter 146. Inthe illustrated example, the voltage sensor 167 is implemented as a DCvoltage sensor 167 _(DC) that measures a voltage of the capacitance 145and as an AC voltage sensor 167 _(AC) that measures a voltage on onephase of the motor-generator 144, these two components of the voltagesensor 167 being integrated within the ECU 164. Use of external voltagesensors operatively connected to the ECU 164 is also contemplated. Athird subsystem 706 includes the capacitance 145, as well as a chargingcircuit 705 and a discharging circuit 707 that respectively use thedrivers 216 and 217 and the transistors Q1 and Q2 of FIG. 8 to controlcharging and discharging of the capacitance 145.

The circuit 700 operates at a nominal system voltage, which is typicallythe voltage of the capacitance 145 when fully charged. A fourthsubsystem 708 includes components of the snowmobile 10 that operate atthe system voltage. These components may include the direct fuelinjectors 132 a, 132 b, an electric oil pump 710, ignition coils 712 forthe spark plugs 134 a, 134 b, and a fuel pump 714. A fifth subsystem 716includes accessories of the snowmobile 10 that operate at an accessoryvoltage. These accessories may include a multi-port fuel injector (MPFI)718, lighting 720, an instrument cluster 722 including the display 186,heated grips 724 mounted on the handlebar 36 and an exhaust valve 726.The DC-DC convertor 704 converts the system voltage to the accessoryvoltage and thus provides electric power to the accessories.

In an implementation, the circuit 700 normally operates at a systemvoltage of 55 volts and some accessories of the snowmobile normallyoperate at an accessory voltage of 12 volts. The various sensors 167,170, 171, 172, 174, 176 and 182 may operate at the system voltage or atthe accessory voltage, or at any other voltage if an additional voltageconverter (not shown) is included in the circuit 700. In thisimplementation, the DC-DC converter 704 is a 55V-12V converter. Thesevalues for the system voltage and for the accessory voltage are nominalfor this implementation and may vary according to the actual operatingconditions of the snowmobile 10.

FIG. 15 is a timing diagram showing an example of a sequence forchanging the control strategy for the delivery of electric power betweenthe capacitance 145 and the motor-generator 144 along with correspondingengine rotational speed variations. A graph 410 shows a variation ofelectrical power delivery control strategies applied by the ECU 164, asa function of time, in seconds. In this graph 410, “Strategy 1”indicates the application of the first control strategy, specificallyusing a vector control, “Strategy 2” indicates the application of thesecond control strategy, which uses shunting of phases of themotor-generator 144 to control the voltage applied to charge thecapacitance 145, and “Neutral” indicates the application of the neutralcontrol mode. In the neutral control mode, the voltage generated by themotor-generator 144 may simply be converted to direct current andapplied to charge the capacitance 145, provided that a peak backelectromotive force voltage of the motor-generator 144 is higher thanthe nominal voltage of the circuit 200, a condition that is usually metwhen the ICE 24 reaches a sufficient revolution speed. A graph 412 showsa corresponding variation of a rotational speed of the crankshaft 100over a same time scale. In a first half-second of operation followingthe user command for the electric start procedure for the ICE 24, nopower is delivered between the capacitance 145 and the motor-generator144. This period is used to equalize the voltages of the capacitance 145and of the capacitor C1. The actual duration of this period may varyconsiderably as a function of the value of the capacitor C1. A periodranging from 0.5 to about 1.1 seconds corresponds essentially to theperiod covered between 0 and 0.4 seconds on the graphs 400 and 402. TheECU 164 uses the first control strategy (Strategy 1) to control deliveryof electric power from the capacitance 145 to the motor-generator 144until the ICE 24 is actually started. Then, between 1.1 and 1.3 seconds,as the ICE 24 accelerates, electric power is delivered from themotor-generator 144 to the capacitance 145 in the neutral control mode.When the crankshaft 100 reaches a sufficient rotational speed, at about1.3 seconds, the motor-generator 144 starts generating power at avoltage that tends to exceed the nominal voltage of the capacitance 145.This is when the ECU 164 starts using the second control strategy(Strategy 2) to control delivery of electrical power from themotor-generator 144 to the capacitance 145 and to various electric loads(not shown) of the vehicle. A variant in which the neutral control modeis not implemented is also contemplated, in which the ECU 164 startsusing the second control strategy as soon as the ICE 24 is successfullystarted.

FIG. 16 is another timing diagram showing an example of an impact of thecontrol strategies on a current exchanged between the capacitance andthe ETM and on a system voltage. A graph 420 shows a voltage of one ofthe Phases A, B or C of the motor-generator 144 as a function of time,in seconds, and as a function of the control strategies. In the firstcontrol strategy, the ECU 164 controls the application of voltage pulsesto the motor-generator 144 in pulse width modulation (PWM) mode, at avery rapid rate typically expressed in kilohertz. Then, as ignition ofthe ICE 24 beings, in the neutral control mode, the motor-generator 144starts generating voltage on its own, this voltage increasing until themode changes to the second control strategy, the voltage cycling at arate that follows the rotation of the crankshaft 100. It may be observedthat because of the configuration of the inverter 146, the voltage oneach phase of the motor-generator alternates between zero (0) volt andthe nominal system voltage without cycling through negative values. Agraph 422 shows a variation of a current flowing between the capacitance145 and the motor-generator 144 as the ECU 164 changes from the firstcontrol strategy to the neutral control mode to the second controlstrategy. Initially, in the first control strategy, a three-phasecurrent flows from the capacitance 145 toward the motor-generator 144,through the inverter 146. For most of the neutral control strategy, alltransistors T1-T6 of the inverter are open and no current flows betweenthe capacitance 145 and the motor-generator 144. Significant current isgenerated by each phase of the motor-generator 144 after the start ofthe ICE 24. The ECU 164 applies shunting of the phases of themotor-generator 144 for preventing excess voltage at its output, asillustrated by the strong variations of the current in the right-handpart of graph 422. The graph 424 shows an actual voltage measured on thecapacitance 145 as the ECU 164 changes from the first control strategyto the neutral control mode to the second control strategy. The voltageof the capacitance 145 initially decreases while electric power isdelivered to the motor-generator 145. Following ignition of the ICE 24,the ECU 164 places the system in neutral control mode. A discharge ofthe freewheel diodes D1-D6 causes a modest increase of the voltage ofthe capacitance 145. Opening of the transistor Q2 at the beginning ofthe operation in the second control strategy temporary isolates thecapacitance 145 from the motor-generator so that electric power producedby the motor-generator is mainly available for other needs of thesystem, such as injection, ignition, control, and the like. Closing ofthe transistor Q1 allows charging of the capacitance 145, with a voltagethat oscillates near the nominal system voltage according to theshunting of the motor-generator 144.

The timing values, rotational speed values, and torque valuesillustrated in the various graphs 400, 402, 410, 412, 420, 422 and 424are provided for illustration and do not limit the present disclosure.Actual values may depend greatly on the construction of the ICE 24, ofthe motor-generator 144, of the capacitance 145 and on the operationstrategy of the ECU 164.

Particular Application of the First Control Strategy

An implementation of the first control strategy, applicable in both theelectric start procedure and the assisted start procedure, will now bedescribed. As expressed hereinabove, the present snowmobile 10 (or othervehicle constructed according to the teachings of the presentdisclosure) includes the ICE 24 equipped with the motor-generator 144operatively connected to the crankshaft 100, the capacitance 145, theECU 164, one direct fuel injector 132A, 132B in each cylinder 106A,106B, and the ACPS 170 or an equivalent sensor that enables the ECU 164to be constantly aware of the absolute angular position of thecrankshaft 100, as long as the ACPS 170 and the ECU 164 are energized.

In an implementation where the ICE 24 is not equipped with adecompression system, the capacitance 144 and the motor-generator 145may not be able to generate sufficient torque to rapidly expel gasesremaining in the combustion chambers 120A, 102B after the ICE 24 hasstopped. For that reason, an implementation initially applies a lowlevel of torque to the crankshaft 100 in order to cause the pistons116A, 116B to slowly force remaining gases out of the combustionchambers 120A, 120B. When a sufficient portion of the gases have beenexpelled, a higher level of torque is applied to the crankshaft 100 tobring one of the pistons 116A, 116B at its TDC position and beyond, inorder to start the ICE 24. In another implementation where the ICE 24 isequipped with a decompression system (not shown), or in a furtherimplementation where the capacitance 145 and the motor-generator 144have sufficient torque generating capabilities, the higher level oftorque can optionally be applied to the crankshaft throughout theprocedure.

In an implementation without a decompression system, when the ICE 24 isstopped, the pistons 116A, 116B rapidly slow down and tend to terminatetheir motion substantially at a natural point where pressure in thecombustion chambers 120A, 120B is fairly low. In a two-cylinder engine,one of the pistons 116A or 116B usually stops at about 100 to 80 degreesbefore TDC because of the configuration of the main and auxiliaryexhaust ports 136A, 136B, 138A, 138B. When the ICE 24 starts again, thatpiston 116A or 116B initially rotates by moving up, toward its TDCposition. In an implementation as shown for example on FIGS. 4A and 4B,the upward movement of the piston (piston 116B on FIGS. 4A and 4B) tendsto push gases remaining in the combustion chamber 120B to exit throughthe main exhaust port 136B and through the auxiliary exhaust port 138B,some of the remaining gases also passing around the at least one ring117B of the piston 116B, until the piston 116B arrives at about 50 to 0degrees before TDC. Because the exhaust ports 136B, 138B are initiallyopen, until about 60 degrees before TDC, this movement of the piston116B requires very little energy. At the same time, the opposite piston116A is moving away from its TDC position and is not compressing,therefore that movement of the opposite piston 116A is also made withvery little energy.

After the exhaust ports 136B, 138B have closed, the piston 116B startscompressing any remaining gases in the combustion chamber 120A, a modestportion of the remaining gases being expelled around the at least onering 117A of the piston 116B. More effort is needed to continue rotatingthe crankshaft 100 and more torque is applied starting when the piston117B is at about 50 to 0 degrees before TDC.

Immediately after having passed its TDC position, the piston 116B is ina proper position for combustion. Owing to the absolute angular positionof the crankshaft 100 provided by the ACPS 170, the moment when thepiston 116B is at its TDC position is known with sufficient accuracy forthe ECU 164 to control injection of an amount of fuel, which may in partbe calculated in view of readings from one or more of the varioussensors 167, 170, 171, 172, 174, 176 and 182, in the combustion chamber120B by the direct fuel injector 132B when the piston 116B is in a rangebetween about 3 degrees before TDC until 7 degrees after TDC and tocontrol ignition of the fuel by the spark plug 134B thereafter, beforethe piston 116B passes again at its TDC position, for example at about 0to 12 degrees after TDC.

FIG. 17 is yet another timing diagram showing an example of a variationof torque applied to the ETM during the first control strategy. A graph430 shows a variation of a torque delivered to the motor-generator 144as a function of time, in seconds. The graph 430 is not to scale.Operation of the ICE 24 in the period shown on the graph 430 is in thefirst control strategy as delivery of electric power is from thecapacitance 145 to the motor-generator 144.

Control of the level of torque applied to the motor-generator 144 may beeffected by controlling a current applied through the inverter 146 tothe motor-generator 144. To this end, the vector control techniquedescribed hereinabove, including any one of its variant, may use theabsolute angular position of the crankshaft 100 to deduce an absoluteangular position of the rotor 150 of the motor-generator 144, which inturn is used as a basis to control the current and, consequently, thelevel of torque applied by the motor-generator 144 on the crankshaft100. Referring again to FIG. 13, the absolute angular position of thecrankshaft 100 is provided encoded as signals u_(A), u_(S) 514 areapplied to a quadrature timer 516 of the vector control drive 500.

In an implementation of the electric start procedure, the ICE 24 isstopped at an initial time t₀ (0 sec.) and operations 300, 302, 304,322, 306, 308 and 310 depicted on FIG. 9 (some of which are optional)have just been completed. In an implementation of the assisted startprocedure, the user has initiated a rotation of the crankshaft 100.Operations 600, 602, 604, 606, 608, 610, 612 depicted on FIG. 11 (someof which are optional) have just been completed at the initial time t₀.In either cases, the ACPS 170 is energized and ready to sense theabsolute angular position of the crankshaft 100 (or, alternatively, anabsolute position sensor is sensing the angular position of a componentof the ICE 24 that turns in synchrony with the crankshaft 100, forexample the sensor 177 sending the angular position of the water pump173), either at operation 324, in the case of the electric startprocedure, or at operation 624 in the case of the assisted startprocedure. From this point, the sequence shown on graph 430 applies toeither procedure. As expressed hereinabove, in a two-cylinder engine,one of the pistons 116A, 116B usually stops at a predetermined position,about 100 to 80 degrees before TDC, when stopping the ICE 24 and thiscondition is present at the initial time t₀.

In response to a user command to start the ICE 24, the command being inthe form of an actuation of the electric start switch 168 or in the formof a pull on the rope 158 of the recoil starter 156, the ECU 164controls the start of electric power delivery to the motor-generator 144in order to rotate the crankshaft 100. The vector control drive 500controls a level of torque applied on the rotor 150 of themotor-generator 144. The torque is first delivered at a modest level εfrom the initial time t₀, where the piston 116B is at about 100 to 80degrees before TDC. The torque increases toward a level a until time t₁when the piston is at about 50 to 0 degrees before TDC. At that time,the piston 116b effectively blocks the exhaust ports 136B and 138B andany gas remaining in the combustion chamber 120B will either becompressed, or expelled at a reduced rate around the at least one ring117B. From this time t₁, the vector control drive 500 controls deliveryof torque at a higher level β. Shortly thereafter, at time t₂, thepiston is in a range of about 3 degrees before TDC to 7 degrees afterTDC. The ECU 164 causes the direct fuel injector 132B to inject acalculated amount of fuel into the combustion chamber 120B. Then, attime t₃, the piston 116B being at about 0 to 12 degrees after TDC, theECU 164 causes the spark plug 134B to ignite the fuel in the combustionchamber 120B. This combustion effectively starts the ICE 24 at time t₄in many circumstances.

Of course, starting of the ICE 24 may require continued application oftorque on the crankshaft 100 by the motor-generator 144, as well asinjection and ignition of fuel in the combustion chambers 120A, 120B, ina few cycles of operations 326, 328, 330 and 332 of FIG. 9, or in a fewcycles of operations 626, 628, 630 and 632 of FIG. 11. The ICE 24 isdeemed started at time t₅ when the crankshaft reaches a predeterminedrevolution threshold, for example 600 RPM. The ICE 24 is now in theneutral control mode.

The torque level a from the initial time t₀ until the time t₁ may beconstant. In the example of FIG. 17, the electric power is firstdelivered from the capacitance 145 to the motor-generator 144 at agradually increasing rate, providing a torque increasing from a lowlevel ϑ (which may be zero or slightly above zero) until the level oftorque α, in a range of one to ten newton-meters (1 to 10 Nm), isreached at time t₁. When the piston 116B is at about 50 to 0 degreesbefore TDC at time t₁, the torque is applied at the higher level βsufficient to propel the piston 116B beyond its TDC position, forexample in a range of 10 to 15 Nm. In an implementation, the level ofelectric power that provides this torque value β corresponds to amaximum power delivery capability of the capacitance 145. In the same oranother implementation, the level of electric power that provides thistorque value β corresponds to a maximum power torque value that themotor-generator 144 can withstand. The torque values described hereinand timing values shown on FIG. 17 are provided as examples and do notlimit the present disclosure. In an implementation where the ICE 24 isequipped with a decompression system, the torque may be applied at thehigher level β starting from the initial time t_(o) until the ICE 24 isproperly started.

FIG. 18 is a sequence diagram showing operations of a method forstarting an internal combustion engine. A sequence shown in FIG. 18comprises a plurality of operations, some of which may be executed invariable order, some of the operations possibly being executedconcurrently, and some of the operations being optional. The sequence ofFIG. 18 is implemented in the ICE 24 which has the motor-generator 144operatively connected to the crankshaft 100. The sequence corresponds,in one implementation, to operations 324, 326, 328 and 330 of FIG. 9and, in the same or another implementation, to operations 624, 626, 628and 630 of FIG. 11. In order to ease the illustration and without lossof generality, the sequence is described in a case where the piston 116Bis at a predetermined position of about 100 to 80 degrees before TDC, ata time where one of the electric start or assisted start procedure isinitiated by the user. The crankshaft 100 is at the time not rotating(electric start procedure) or just barely starting to rotate (assistedstart procedure). Initial injection and ignition will take place in thecombustion chamber 120B corresponding to the piston 116B. At that time,the opposite piston 116A is at about 80 to 100 degrees after TDC andwill initially move away from TDC, not compressing any gas in thecombustion chamber 120A.

The sequence starts at operation 800 when an absolute position sensor,for example the ACPS 170, is energized so to be able determine theabsolute angular position of the crankshaft 100 when the ICE 24 isstopped or starting to rotate. The ACPS 170 will continue beingenergized when the crankshaft 100 is rotating. An absolute angularposition of the crankshaft 100 is determined at operation 802, theabsolute angular position of the crankshaft 100 being related to a TDCposition of the piston 116B in the combustion chamber 120B of the ICE24. As expressed hereinabove, the ACPS 170 may be substituted by anotherabsolute angular position sensor (not shown) that senses an absoluteangular position of a component of the ICE 24 that rotates in synchronywith the crankshaft 100. In any case, the ECU 164 calculates theabsolute angular position of the crankshaft 100 based on a readingprovided by the ACPS 170 or based on the sensed absolute angularposition of the component of the ICE that rotates in synchrony with thecrankshaft 100. At operation 804, when the ICE 24 is not equipped with adecompression system, electric power starts being delivered from thecapacitance 145 to the motor-generator 144 at a first level to rotatethe crankshaft 100. Optionally, the operation 804 may include asub-operation 806 in which the delivery of electric power to themotor-generator 145 gradually increases from an initial level ϑ to thefirst level, as illustrated on FIG. 17 between times t₀ and t₁. Thefirst level, and in particular the initial level ϑ and a slope of thepower delivery between times t₀ and t₁ may be determined based on theinitial angular position of the crankshaft 100. The first level ofelectric power delivery is calculated so that the motor-generator 145generates sufficient torque to rotate the crankshaft 100 until thepiston 116B reaches a predetermined position before the TDC position,for example between 50 to 0 degrees before TDC. At operation 808,electric power is then delivered from the capacitance 145 to themotor-generator 144 at a second level greater than the first level whenthe piston reaches 116B the predetermined position before the TDCposition. The second level of electric power delivery is calculated sothat the motor-generator 145 generates sufficient torque to cause thepiston to move beyond the TDC position. In more details, the vectorcontrol drive 500 deduces an angular position of the rotor 150 of themotor-generator 145 from the angular position of the crankshaft 100. Theangular position of the rotor 150 is used in the vector control drive500 to calculate, at first, the torque value sufficient to bring thepiston 116B to the predetermined position before the TDC position andthen to calculate the torque value sufficient to cause the piston tomove beyond the TDC position. The first and second levels of electricpower delivery are calculated based on these torque values.

In an implementation of the ICE 24 equipped with a decompression system,electric power may be delivered by the capacitance 145 to themotor-generator 144 already at the second level in the course ofoperation 804. In that case, operations 804 and 808 may be considered asessentially merged into a same operation.

In any case, fuel is injected at operation 810 in the combustion chamber120B of the ICE 24 after the piston 116B has passed beyond the TDCposition a first time. In an implementation, injection takes place in arange of about 3 degrees before TDC to 7 degrees after TDC. Given thatfuel has been directly injected in the combustion chamber 120B, the fuelis immediately available in the combustion chamber 120B. Consequently,the fuel is ignited without delay at operation 812. A timing of theignition operation 812 may vary but will take place before the piston116B passes the TDC position a second time. In one implementation,ignition takes place before a downward motion of the piston 116B causesan opening of the exhaust ports 136B, 138B, as the crown of the piston116B reaches the top of a first one of the exhaust ports 136B, 138B. Inanother implementation, ignition takes place about 2 degrees of rotationafter injection, in a range of 0 to 12 degrees after TDC.

Frequently, the ICE 24 will start after performing the injection andignition operations 810 and 812 a single time. This will be determinedat operation 330 of FIG. 9, in the case of an electric start, or atoperation 630 of FIG. 11, in the case of an assisted start, by detectingthat a rotational speed of the crankshaft 100 calculated by the ECU 164based on readings form the CPS 171 has reached a minimum threshold. Thedelivery of electric power to the motor-generator 144 is stopped atoperation 814 after starting the ICE 24. In cases where the ICE 24 isnot started after operation 812, the sequences of FIG. 9 or 11, asapplicable, may continue.

FIG. 19 is a sequence diagram showing operations of a method forcontrolling delivery of electric power between a power source and theETM. A sequence shown in FIG. 19 comprises a plurality of operations,some of which may be executed in variable order, some of the operationspossibly being executed concurrently, and some of the operations beingoptional. The sequence of FIG. 19 is implemented in the ICE 24 which hasthe motor-generator 144 electrically connected to the capacitance 145,as shown for instance on FIG. 8. The sequence may start at operation 902when a start signal 221 is applied to transistor Q2, which is a start-uppower electronic switch, to cause turning on of transistor Q2, allowingdelivery of electric power from the capacitance 145 to themotor-generator 144 via the transistor Q2. As shown on FIG. 8, the startsignal 221 may be applied to the driver 217 that, in turn, applies thestart signal to the transistor Q2. Application of the start signal 221may be terminated at operation 904, turning off the transistor Q2 beforethe next operation. Then at operation 906, a recharge signal 222 isapplied to the transistor Q1, which is a run-time power electronicswitch, to cause turning on of the transistor Q1, allowing delivery ofelectric power from the motor-generator 144 to the capacitance 145 viathe transistor Q1 and, optionally, via the current limiting circuit 224.The recharge signal 222 may be applied to the driver 216 that, in turn,applies the recharge signal to the transistor Q1.

In an implementation, the transistor Q2 is repeatedly turned on and offat operation 902 for instance by repeatedly applying and releasing thestart signal 221 to the driver 217, in order to limit the delivery ofelectric power from the capacitance 145 to the motor-generator 144. In avariant, this repeated application and release of the start signal 221is performed under the control of the ECU 164 according to a PWM mode.

In an implementation in which the capacitor C1 and the current limitingcircuit 224 are provided, operation 900 may precede operation 902. Inoperation 900, an initiation signal 220 is briefly applied and thenreleased to turn on the transistor Q1 so that the capacitance 145 startscharging the capacitor C1 while the current limiting circuit 224protects the transistor Q1 from excessive current flowing therethrough.As soon as a voltage starts being established in the capacitor C1,operation 900 ends, causing the transistor Q1 to turn off, and thesequence continues with operation 900 as expressed hereinabove.

The methods, systems and internal combustion engines implemented inaccordance with some non-limiting implementations of the presenttechnology can be represented as follows, presented in numbered clauses.

Modifications and improvements to the above-described implementations ofthe present technology may become apparent to those skilled in the art.For example, it is contemplated that the ICE 24 could be provided with adecompression system. The decompression system can release pressure inthe combustion chambers 120A, 120B, thereby reducing compression forcesthat need to be overcome by the motor-generator 144 at operations 326and 626 described above. Therefore, by providing a decompression system,it is contemplated that the motor-generator 144 could be even smallerand lighter, a size and a weight of the capacitance 145 being reducedaccordingly. Also, when a decompression system is provided, the sequenceof FIG. 18 may be modified by delivering electric power to themotor-generator already at the higher, second level starting atoperation 804. The foregoing description is intended to be exemplaryrather than limiting. The scope of the present technology is thereforeintended to be limited solely by the scope of the appended claims.

Clauses

-   [Clause 1] A method for starting an internal combustion engine (ICE)    having a crankshaft and an electric turning machine (ETM)    operatively connected to the crankshaft, the method comprising:

determining an absolute angular position of the crankshaft, the absoluteangular position of the crankshaft being related to an angular positionof a rotor of the ETM;

delivering electric power to the ETM at a first level to rotate thecrankshaft; and

delivering electric power to the ETM at a second level greater than thefirst level when the rotor of the ETM reaches a predetermined angularposition.

-   [Clause 2] The method of clause 1, further comprising:

calculating the first level of electric power delivery so that the ETMgenerates sufficient torque to rotate the crankshaft until the rotorreaches the predetermined angular position; and

calculating the second level of electric power delivery so that the ETMgenerates sufficient torque to rotate the crankshaft beyond thepredetermined angular position of the rotor.

-   [Clause 3] The method of clause 2, wherein:

calculating the first level of electric power delivery comprises using avector control of the delivery of electric power at the first levelbased on a predetermination of the sufficient torque to rotate thecrankshaft until the rotor reaches the predetermined angular position;and

calculating the second level of electric power delivery comprises usinga vector control of the delivery of electric power at the second levelbased on a predetermination of the sufficient torque to rotate thecrankshaft beyond the predetermined angular position of the rotor.

-   [Clause 4] The method of any one of clauses 1 to 3, further    comprising energizing an absolute position sensor used to determine    the absolute angular position of the crankshaft when the ICE is    stopped.-   [Clause 5] The method of clause 4, further comprising energizing the    absolute position sensor when the crankshaft is rotating.-   [Clause 6] The method of any one of clauses 1 to 5, further    comprising gradually increasing the delivery of electric power to    the ETM from an initial level to the first level before delivering    electric power to the ETM at the second level.-   [Clause 7] The method of any one of clauses 1 to 6, wherein the    absolute angular position of

the crankshaft is further related to a position of a piston in acombustion chamber of the ICE in relation to a top dead center (TDC)position of the piston.

-   [Clause 8] The method of clause 7, wherein:

delivering electric power to the ETM at the second level starts when thepiston reaches a predetermined position before the TDC position; and

the method further comprises injecting fuel in the combustion chamber ofthe ICE when the piston passes the TDC position a first time andigniting the fuel in the combustion chamber.

-   [Clause 9] The method of clause 8, further comprising determining    the first level of the electric power delivered to the ETM based on    an initial angular position of the crankshaft.-   [Clause 10] The method of clause 9, wherein the initial angular    position of the crankshaft is a position of the crankshaft when the    ICE is stopped.-   [Clause 11] The method of any one of clauses 9 or 10, wherein the    initial angular position is in a range between 80 and 100 degrees    before the TDC position.-   [Clause 12] The method of any one of clauses 8 to 11, wherein    delivering the electric power to the ETM before the piston reaches    the predetermined position before the TDC position causes gases to    be expelled from the combustion chamber.-   [Clause 13] The method of clause 12, wherein the predetermined    position before the TDC position is determined according to a    configuration of exhaust ports of the ICE.-   [Clause 14] The method of any one of clauses 8 to 13, wherein the    predetermined position before the TDC position in a range between 0    and 50 degrees before the TDC position.-   [Clause 15] The method of any one of clauses 8 to 14, further    comprising terminating the delivery of electric power to the ETM    after starting the ICE.-   [Clause 16] The method of clause 15, wherein the delivery of    electric power to the ETM is terminated when a rotational speed of    the crankshaft reaches a minimum threshold.-   [Clause 17] The method of any one of clauses 8 to 16, wherein the    fuel is ignited before the piston passes the TDC position a second    time.-   [Clause 18] The method of any one of clauses 8 to 17, wherein the    fuel is injected in the combustion chamber when the position of the    piston passes a range between 3 degrees before the TDC position and    7 degrees after the TDC position.-   [Clause 19] The method of any one of clauses 8 to 18, wherein the    fuel is ignited when the position of the piston is in a range    between 0 and 12 degrees after the TDC position, ignition of the    fuel taking place after injection of the fuel.-   [Clause 20] The method of any one of clauses 8 to 19, wherein    ignition takes place before the piston reaches the top of an exhaust    port in the combustion chamber of the ICE-   [Clause 21] The method of any one of clauses 8 to 20, wherein:

the first level of electric power delivery is calculated so that the ETMgenerates sufficient torque to rotate the crankshaft until the pistonreaches the predetermined position before the TDC position; and

the second level of electric power delivery is calculated so that theETM generates sufficient torque to cause the piston to move beyond theTDC position.

-   [Clause 22] The method of any one of clauses 1 to 21, wherein    determining the absolute angular position of the crankshaft    comprises sensing the absolute angular position of the crankshaft.-   [Clause 23] The method of any one of clauses 1 to 21, further    comprising:

sensing an absolute angular position of a component of the ICE thatrotates in synchrony with the crankshaft, wherein the component of theICE that rotates in synchrony with the crankshaft is selected from therotor of the ETM, a fuel pump, an oil pump, a water pump, a camshaft,and a balance shaft; and

calculating the absolute angular position of the crankshaft based on thesensed absolute angular position of the component of the ICE thatrotates in synchrony with the crankshaft.

-   [Clause 24] A system for starting an internal combustion engine    (ICE) having a crankshaft, the system comprising:

a power source;

an electric turning machine (ETM) adapted for being mounted to thecrankshaft;

an absolute position sensor adapted for providing an indication of anabsolute angular position of the crankshaft, the absolute angularposition of the crankshaft being related to an angular position of arotor of the ETM; and

an engine control unit (ECU) operatively connected to the absoluteposition sensor, the ECU being adapted for determining the absoluteangular position of the crankshaft based on the indication provided bythe absolute position sensor, the ECU being further adapted forcontrolling:

-   -   a delivery of electric power from the power source to the ETM at        a first level to rotate the crankshaft;    -   a delivery of electric power from the power source to the ETM at        a second level greater than the first level when the rotor of        the ETM reaches a predetermined angular position.

-   [Clause 25] The system of clause 24, wherein the ECU is further    adapted for:

calculating the first level of electric power delivery so that the ETMgenerates sufficient torque to rotate the crankshaft until the rotorreaches the predetermined angular position; and

calculating the second level of electric power delivery so that the ETMgenerates sufficient torque to rotate the crankshaft beyond thepredetermined angular position of the rotor.

-   [Clause 26] The system of clause 25, wherein:

the ECU implements a vector control of the delivery of electric power atthe first level based on a predetermination of the sufficient torque torotate the crankshaft until the rotor reaches the predetermined angularposition; and

the ECU implements a vector control of the delivery of electric power atthe second level based on a predetermination of the sufficient torque torotate the crankshaft beyond the predetermined angular position of therotor.

-   [Clause 27] The system of any one of clauses 24 to 26, wherein the    absolute angular position of the crankshaft is further related to a    position of a piston in a combustion chamber of the ICE in relation    to a top dead center (TDC) position of the piston.-   [Clause 28] The system of clause 27, wherein:

the delivery of electric power from the power source to the ETM at thesecond level starts when the piston reaches a predetermined positionbefore the TDC position; and

the ECU is further adapted for controlling an injection of fuel in thecombustion chamber of the ICE when the piston passes the TDC position afirst time, and for controlling ignition of the fuel in the combustionchamber.

-   [Clause 29] The system of any one of clauses 24 to 28, wherein the    ETM is adapted for being coaxially mounted to the crankshaft.-   [Clause 30] The system of any one of clauses 24 to 29, wherein the    absolute position sensor is adapted for sensing the absolute angular    position of the crankshaft.-   [Clause 31] The system of any one of clauses 24 to 29, wherein:

the absolute position sensor is adapted for sensing an angular positionof a component of the ICE that rotates in synchrony with the crankshaft,wherein the component of the ICE that rotates in synchrony with thecrankshaft is selected from the rotor of the ETM, a fuel pump, an oilpump, a water pump, a camshaft, and a balance shaft; and

the ECU is adapted for calculating the absolute angular position of thecrankshaft based on the sensed absolute angular position of thecomponent of the ICE that rotates in synchrony with the crankshaft andbased on a mechanical relationship between the crankshaft of thecomponent of the ICE that rotates in synchrony with the crankshaft.

-   [Clause 32] The system of any one of clauses 24 to 31, wherein the    absolute position sensor is permanently connected to the power    source.-   [Clause 33] The system of any one of clauses 24 to 31, wherein the    absolute position sensor is energized by the power source at the    onset of a start procedure for the ICE.-   [Clause 34] An internal combustion engine (ICE) comprising:

a crankshaft;

a first cylinder;

a cylinder head connected to the first cylinder;

a piston operatively connected to the crankshaft and disposed in thefirst cylinder, the first cylinder, the cylinder head and a crown of thefirst piston defining a first variable volume combustion chambertherebetween; and

the system of any one of clauses 24 to 33, wherein the absolute angularposition of the crankshaft is related to a position of the first pistonin the first combustion chamber.

-   [Clause 35] The ICE of clause 34, further comprising:

a direct fuel injector operatively connected to the ECU; and

an ignition system operatively connected to the ECU;

wherein the ECU is adapted for causing the direct fuel injector toinject the fuel in the first combustion chamber and for causing theignition system to ignite the fuel.

-   [Clause 36] The ICE of any one of clauses 34 or 35, further    comprising:

a second cylinder; and

a second piston operatively connected to the crankshaft and disposed inthe second cylinder, the second cylinder, the cylinder head and a crownof the second piston defining a second variable volume combustionchamber therebetween;

wherein when the first piston compresses gases in the first combustionchamber, the second piston expands the volume of the second combustionchamber.

-   [Clause 37] A method for starting an internal combustion engine    (ICE) having a crankshaft and an electric turning machine (ETM)    operatively connected to the crankshaft, the method comprising:

energizing an absolute position sensor adapted for providing anindication of an angular position of a rotor of the ETM; and

applying a current to the ETM to generate a sufficient torque to rotatethe crankshaft.

-   [Clause 38] The method of clause 37, wherein:

the absolute position sensor provides the indication of the angularposition of the rotor of the ETM in signals sent to a controller; and

the controller calculates on an ongoing basis the actual angularposition of the rotor of the ETM based on the signals from the absoluteposition sensor.

-   [Clause 39] The method of any one of clauses 37 or 38, wherein    applying a current to the ETM further comprises:

initially applying a first current to the ETM; and

subsequently applying to the ETM a second current greater than the firstcurrent when the angular position of the rotor of the ETM passes beyonda predetermined angular position.

-   [Clause 40] The method of any one of clauses 37 to 39, further    comprising receiving at a controller a start command for the ICE.-   [Clause 41] The method of any one of clauses 37 to 40, further    comprising:

determining an initial angular position of the rotor of the ETM; and

determining a first amount of torque to be supplied by the ETM to thecrankshaft based in part on the initial angular position of the rotor ofthe ETM.

-   [Clause 42] The method of clause 41, further comprising:

determining a second angular position of the rotor of the ETM, thesecond angular position indicating that the rotor of the ETM has passeda first predetermined angular position; and

determining a second amount of torque to be supplied by the ETM to thecrankshaft based in part on the second angular position of the rotor ofthe ETM, the second amount of torque being greater than the first amountof torque.

-   [Clause 43] The method of clause 42, further comprising:

determining a third angular position of the rotor of the ETM, the thirdangular position indicating that the rotor of the ETM has passed asecond predetermined angular position, the second predetermined angularposition being a top dead center (TDC) position of a piston within acombustion chamber; and

injecting fuel in the combustion chamber of the ICE.

-   [Clause 44] The method of clause 43, further comprising:

determining a fourth angular position of the rotor of the ETM, thefourth angular position indicating that the rotor of the ETM has passeda third predetermined angular position, the third predetermined angularposition being after the second predetermined angular position; and

igniting the fuel in the combustion chamber of the ICE.

-   [Clause 45] The method of clause 44, wherein the fourth angular    position is less than 110 degrees of rotation of the crankshaft    beyond the initial angular position.-   [Clause 46] The method of clause 44, wherein the fourth angular    position is selected so that ignition takes place before opening of    an exhaust port in the combustion chamber of the ICE.-   [Clause 47] An internal combustion engine (ICE), comprising:

a crankshaft;

a cylinder head defining in part a variable combustion chamber of theICE;

a direct fuel injector mounted on the cylinder head;

a power source;

an electric turning machine (ETM) adapted for rotating the crankshaft;

an absolute position sensor adapted for providing an indication of anangular position of a rotor of the ETM; and

an engine control unit (ECU) operatively connected to the absoluteposition sensor, the ECU being adapted for:

-   -   vector controlling a delivery of electric power from the power        source to the ETM based on the angular position of the rotor of        the ETM; and    -   causing the direct fuel injector to inject fuel directly in the        combustion chamber at a time selected based on the angular        position reached by the rotor of the ETM.

-   [Clause 48] The ICE of clause 47, wherein the ECU causes the    delivery of electric power from the power source to the ETM to    generate a first level of torque until the rotor of the ETM reaches    a first predetermined position and then to generate a second level    of torque greater than the first level of torque as the rotor of the    ETM rotates beyond the first predetermined position.

-   [Clause 49] The ICE of clause 48, wherein the ECU causes the direct    fuel injector to inject fuel directly in the combustion chamber    after the ETM has reached the first determined position.

-   [Clause 50] The ICE of clause 49, wherein the absolute angular    position of the rotor of the ETM is related to a position of a    piston in the combustion chamber, injection of the fuel taking place    when the piston passes at a top dead center position within the    combustion chamber.

-   [Clause 51] The ICE of clause 50, wherein the ECU causes an ignition    of the fuel after injection of the fuel.

-   [Clause 52] A method for controlling delivery of electric power    between a power source and an electric turning machine (ETM), the    method comprising:

applying a start signal to a start-up power electronic switch to causeturning on of the start-up power electronic switch and to allow deliveryof electric power from the power source to the ETM via the start-uppower electronic switch; and

applying a recharge signal to a run-time power electronic switch tocause turning on of the run-time power electronic switch and to allowdelivery of electric power from the ETM to the power source via therun-time power electronic switch.

-   [Clause 53] The method of clause 52, further comprising ceasing    application of the start signal to the start-up power electronic    switch when applying the recharge signal to the run-time power    electronic switch.-   [Clause 54] The method of any one of clauses 52 or 53, wherein    turning on of the start-up power electronic switch further comprises    repeatedly turning on and off the start-up power electronic switch    to limit the delivery of electric power from the power source to the    ETM.-   [Clause 55] The method of clause 54, wherein the start signal is    repeatedly applied and released to cause repeatedly turning on and    off the start-up power electronic switch.-   [Clause 56] The method of clause 55, wherein the start signal is    varied according to a pulse width modulation mode.-   [Clause 57] The method of any one of clauses 52 to 56, further    comprising providing a current limiting circuit connected in series    with the run-time power electronic switch to limit delivery of    electric power from the ETM to the power source.-   [Clause 58] The method of clause 57, further comprising, before    applying the start signal to the start-up power electronic switch,    applying and then releasing an initiation signal to the run-time    power electronic switch.-   [Clause 59] The method of any one of clauses 52 to 58, wherein the    start signal is applied to the start-up power electronic switch via    a first driver and wherein the recharge signal is applied to the    run-time power electronic switch via a second driver.-   [Clause 60] A circuit comprising:

a discharging circuit comprising a start-up power electronic switchadapted for allowing delivery of electric power from a power source toan electric turning machine (ETM) via the start-up power electronicswitch when the start-up power electronic switch is turned on; and

a charging circuit comprising a run-time power electronic switch adaptedfor allowing delivery of electric power from the ETM to the power sourcevia the run-time power electronic switch when the run-time powerelectronic switch is turned on.

-   [Clause 61] The circuit of clause 60, wherein:

the discharging circuit further comprises a first driver adapted forreceiving a start signal and to forward the start signal to the start-uppower electronic switch; and

the charging circuit further comprises a second driver adapted forreceiving a recharge signal and to forward the recharge signal to therun-time power electronic switch.

-   [Clause 62] The circuit of clause 61, further comprising a control    unit adapted for applying the start signal to the first driver and    for applying the recharge signal to the second driver.-   [Clause 63] The circuit of clause 62, wherein the control unit is    further adapted for ceasing application of the start signal to the    start-up power electronic switch when applying the recharge signal    to the run-time power electronic switch.-   [Clause 64] The circuit of any one of clauses 62 or 63, wherein the    control unit is further adapted for repeatedly applying and    releasing the start signal to the first driver to limit the delivery    of electric power from the power source to the ETM.-   [Clause 65] The circuit of clause 64, wherein the control unit is    further adapted for varying the start signal according to a pulse    width modulation mode.-   [Clause 66] The circuit of any one of clauses 60 to 65, wherein the    charging circuit further comprises a current limiting circuit    connected in series with the run-time power electronic switch and    adapted for limiting delivery of electric power from the ETM to the    power source.-   [Clause 67] The circuit of clause 66, wherein the control unit is    further adapted for applying and then releasing an initiation signal    to the run-time power electronic switch before applying the start    signal to the start-up power electronic switch.

1. A method for starting an internal combustion engine (ICE) having a crankshaft and an electric turning machine (ETM) operatively connected to the crankshaft, the method comprising: determining an absolute angular position of the crankshaft, the absolute angular position of the crankshaft being related to an angular position of a rotor of the ETM; delivering electric power to the ETM at a first level to rotate the crankshaft; and delivering electric power to the ETM at a second level greater than the first level when the rotor of the ETM reaches a predetermined angular position.
 2. The method of claim 1, further comprising: calculating the first level of electric power delivery so that the ETM generates sufficient torque to rotate the crankshaft until the rotor reaches the predetermined angular position; and calculating the second level of electric power delivery so that the ETM generates sufficient torque to rotate the crankshaft beyond the predetermined angular position of the rotor.
 3. The method of claim 2, wherein: calculating the first level of electric power delivery comprises using a vector control of the delivery of electric power at the first level based on a predetermination of the sufficient torque to rotate the crankshaft until the rotor reaches the predetermined angular position; and calculating the second level of electric power delivery comprises using a vector control of the delivery of electric power at the second level based on a predetermination of the sufficient torque to rotate the crankshaft beyond the predetermined angular position of the rotor.
 4. The method of claim 1, further comprising energizing an absolute position sensor used to determine the absolute angular position of the crankshaft when the ICE is stopped.
 5. The method of claim 4, further comprising energizing the absolute position sensor when the crankshaft is rotating.
 6. The method of claim 1, further comprising gradually increasing the delivery of electric power to the ETM from an initial level to the first level before delivering electric power to the ETM at the second level.
 7. The method of claim 1, wherein the absolute angular position of the crankshaft is further related to a position of a piston in a combustion chamber of the ICE in relation to a top dead center (TDC) position of the piston.
 8. The method of claim 7, wherein: delivering electric power to the ETM at the second level starts when the piston reaches a predetermined position before the TDC position; and the method further comprises injecting fuel in the combustion chamber of the ICE when the piston passes the TDC position a first time and igniting the fuel in the combustion chamber.
 9. The method of claim 8, further comprising determining the first level of the electric power delivered to the ETM based on an initial angular position of the crankshaft.
 10. The method of claim 9, wherein the initial angular position of the crankshaft is a position of the crankshaft when the ICE is stopped.
 11. The method of claim 9, wherein the initial angular position is in a range between 80 and 100 degrees before the TDC position.
 12. The method of claim 8, wherein delivering the electric power to the ETM before the piston reaches the predetermined position before the TDC position causes gases to be expelled from the combustion chamber.
 13. The method of claim 12, wherein the predetermined position before the TDC position is determined according to a configuration of exhaust ports of the ICE.
 14. The method of claim 8, wherein the predetermined position before the TDC position in a range between 0 and 50 degrees before the TDC position.
 15. The method of claim 8, further comprising terminating the delivery of electric power to the ETM after starting the ICE.
 16. The method of claim 15, wherein the delivery of electric power to the ETM is terminated when a rotational speed of the crankshaft reaches a minimum threshold.
 17. The method of claim 8, wherein the fuel is ignited before the piston passes the TDC position a second time.
 18. The method of claim 8, wherein the fuel is injected in the combustion chamber when the position of the piston passes a range between 3 degrees before the TDC position and 7 degrees after the TDC position.
 19. The method of claim 8, wherein the fuel is ignited when the position of the piston is in a range between 0 and 12 degrees after the TDC position, ignition of the fuel taking place after injection of the fuel.
 20. The method of claim 8, wherein ignition takes place before the piston reaches the top of an exhaust port in the combustion chamber of the ICE
 21. The method of claim 8, wherein: the first level of electric power delivery is calculated so that the ETM generates sufficient torque to rotate the crankshaft until the piston reaches the predetermined position before the TDC position; and the second level of electric power delivery is calculated so that the ETM generates sufficient torque to cause the piston to move beyond the TDC position.
 22. The method of claim 1, wherein determining the absolute angular position of the crankshaft comprises sensing the absolute angular position of the crankshaft.
 23. The method of claim 1, further comprising: sensing an absolute angular position of a component of the ICE that rotates in synchrony with the crankshaft, wherein the component of the ICE that rotates in synchrony with the crankshaft is selected from the rotor of the ETM, a fuel pump, an oil pump, a water pump, a camshaft, and a balance shaft; and calculating the absolute angular position of the crankshaft based on the sensed absolute angular position of the component of the ICE that rotates in synchrony with the crankshaft. 24-67. (canceled) 